Lee Sin support has been used a few times in pro play in season 4, most commonly in Korea. Both Samsung Galaxy Ozone and Samsung Galaxy Blue have played it. The most famous Lee Sin support player is arguably Mata. Mata is renowned for having 4 accounts in Korean challenger tier, each of which he plays exclusively in different roles. It has been said by Gambit's support EDward that in season 4, with support gold being significantly higher than previous seasons, support players should feel free to pick whichever champs they feel most comfortable on. Lee Sin's rise in popularity as a support was due partly to this way of thinking, along with the fact that rushing Sightstone on Lee is a good idea regardless of role, so it makes sense to play him in a role that requires Sightstone rush. Other benefits of Lee Sin support include his ability to destroy opponents in the lane phase, therefore giving his ADC buddy a big early lead, his lane sustain/spell spam due to being an energy champ and the utility he brings to the table.

Start ward trinket, Relic Shield, Health pots.

First back get Targon.

Rush blue Sightstone (switch to red trinket when you get it).

Merc treads for tenacity, speed and the MR also.

Hydra next for mid game burst damage, sustain and wave clear.

Items after this point are totally situational. You generally want a few tank/utility items to finish off your build such as Randuin's, Visage, Locket, GA, Banshee's. If you are fed, consider getting cleaver after 1 tank item or even straight after Hydra. If you have a few health items, consider finishing Face of the Mountain as sixth item, if not then sell it at some stage.

Get Ruby stone upgrade when you feel you need the extra ward. Depends on play style and the way the game is going.

You need a balance of damage and tanky stats. Too little damage and you can't push the enemy out of lane... Too little defense and they will push you out of lane. Devastating Strikes and Warlord can be dropped for more tanky stats such as Resistance if you feel you need them.

You want flat runes for early lane dominance.

Quints and Marks: Flat AD. Lee has great ratios, so AD benefits him more than armor pen.

Seals: Flat armor for lane trading.

Glyphs: Flat MR for lane trading.

Q: Skill up first for immediate harass and brush check. Max first for harass.

E: Skill up second for early bullying. Max second for the damage, the slow and mid-late game wave clear.

W: Skill up third so you can full combo harass safely. Max last. Can be skilled earlier if for some reason you are behind and need it against particular champs.

R: Skill up 6, 11, 16.

Flash is a must. You need it for next level plays (Though only flash kick if the situation does not permit an Insec).

Ignite is usually the best second summoner, as it gives that added damage threat required to really destroy in lane.

Exhaust is a good pick over ignite in or against certain comps.