Support/Tank Jarvan works a lot like an Alistar tank. You initiate, drop your stuns, slow and other cc's, and just chill until cooldowns are done. Both are really good late game champs. However, unlike Alistar, people have a harder time avoiding Jarvan's initiations and overpowering crowd control. And yes, Support/Tank Jarvan can be the primary tank.

Note: I'm currently in the process of updating this build.

Pros:

Lots of CC
All CC abilities are AoE's
Easy initiations
Easy to last hit (general pro for any Jarvan)
Really strong early game
Ultimate puts positioning in your favor if used correctly
Nice amount of CDR - more knock ups more often.
Lots of auras and debuffs

Cons:

Low mana pool/regen
Less late game health than other tanks, which is bad if they have a lot of ignites or an Olaf
Jarvan's ultimate can work against your team if not used properly
Very little damage output

The Fundamentals: Health, armor, and magic resist is what every tank needs. So Greater Glyph of Magic Resist, Greater Seal of Armor, and Greater Quintessence of Health are the natural choices for a Tank Jarvan. One thing to note, the first item in this build just so happens to be a Ruby Crystal so you may benefit more from an alternative to Health Quints. Of course, you already knew all of this, right?

Marks: Greater Mark of Desolation - ArP is really only for the early game. These bad boys will make you a legitimate threat if the enemy decides too get a little too close.

For obvious reasons, the bulk of my mastery points go into the Defense tree. I put eight points into Utility, increasing mana/health regeneration and maximum mana (which then increases health regeneration even more due to Strength of Spirit ). The last point should go into Cripple, ensuring that you get the most bang for your buck.

[*] I don't invest into dodge because the only time I find that dodge is really useful is when three conditions are met:

1)You don't plan on taking Thornmail
2)The enemy team is reliant on physical, auto-attack champions with high ArP
3)The enemy is lacking in any effective CC (which would make

Mercury's Treads useless; in which case, Boots of Swiftness or Ninja Tabi would be a more viable choice.

Ghost is your bacon and eggs in your breakfast platter of pain. Use this to get in and out of fights effectively. Furthermore, being able to ignore unit collision is wonderful inside your ult.

The more cc the better, right? Use this on carries who extend out of your range or champs like Tryndamere.

Substitutions:
Best used in a 1v2 lane. I find Exhaust and Ghost are needed more often than Teleport.

Heal is a really under-rated spell. Make sure to take the Mender's Faith mastery.

Because this build lacks in damage it may be easy for the enemy team to focus down a tower right under your nose; make sure to take Reinforce if you decide to grab this.

Early game: Try to stay in your lane until you manage to farm 1000 gold. This will buy you a Heart of Gold, Boots, and Cloth Armor. Jarvan has a very quick attack animation, making last hitting a breeze. Use your passive to harass mellee champions and your Dragon Strike to harass both mellee and ranged champions. Save your E/Q combo for kills. At level 6, Jarvan has great gank potential. If the opponent doesn't have flash or a teleport-ability, open up with Cataclysm to give your teammate time to get into position or kill your opponent. If they have flash, save your ult till after they flash. Remember, you will have very little damage, so make sure you talk with your team. Otherwise you'll be wasting mana, health, your ult, and may even give the other team a kill.

Mid Game: Hopefully at this point you should have your Randuin's Omen, Mercury's Treads, and your Quicksilver Sash. The majority of your opponents should have enough natural defenses to shrug off what little damage you'll be doing. I can't stress how important teamwork is from this point off. Now, just because you wont be doing much damage, doesn't mean that you're completely useless. You'll be able to dash through any teamfight tactics the enemy teamfight may try to implement. Don't be afraid to initiate since you can easily back out using your Golden Aegis, Randuin's Omen, and Quicksilver Sash if things turn sour.
Be careful though, this is the most difficult point in a match for Support/Tank Jarvan since you'll be lacking in damage and in any serious amounts of armor or magic resist. You can be focused down pretty quickly by the enemy team.

Late Game: Pretty much like the mid game but without any damage. Instead, you'll be a lot harder to kill. At this point you should have Force of Nature and Frozen Heart. Thanks to you, your team should excel in teamfights so long as you keep your carries alive.

The ideal team: I usually play using this build when my team is primarily composed of carries or lacking in crowd control. Cataclysm has great synergy with Karthus and Heimerdinger. But what about the opposing team? I would suggest using this build when you're playing against a balanced team. In other words, the ol' tank, off-tank/support, 3x carry team.

Cataclysm: You're going to have to initiate with this bad boy. There are many ways of using this ultimate effectively and many ways to use it effectively against your own team. Some guidelines to follow before using Cataclysm:

Try to keep your ultimate away from your team.
Cataclysm also blocks off your allies from coming in; make sure your not saving your enemies.
Don't waste your ult on enemy's being focused down; instead try to block off their tank or close range carries from assisting their team.