Yea Yea I Know What your Thinking, another Fail attempt at making an Attack speed Kassadin there's no way this will work!
That's actually exactly what i thought when i went into my first Dominion Match after numerous attempts of trying to top my team on Average Ability power Kassadin.
The truth is starting off on Kassadin is rough and it takes execution and exploitation of enemies to make him huge. However in Dominion everyone is almost on the same level with items and gold through out the game and you can't exactly be "fed" and continuously destroy the suppressed enemy players.

Pros!
Extremely Mobile
No one Expects you to be Attack Speed
With Sheen and Nether Blade you actually tare through people
No rough start you can go straight into combat from the opening of the field
Never Oom in close quarter combat

Cons!
When Running your hopelessly mana deprived
Can't Stack Riftwalk more than 4 or 5 times (Unless Attacking)
Still Relatively squishy i wouldn't Dive a tower alone.

Magic Pen for Marks; Generic Ability Powered Champs Marks, Don't want your other spells to be completely useless, also Nether blade Scales with Ability power and Deals Magic Damage.

Attack Speed Seals; Your don't generally have a lot of Attack Speed on Kassadin So you should use these, they also increase the speed of mana from Nether Blade making Mp5 seals useless

Ability Power per level Glyph; You level Fats in Dominion and these give you more than the base glyph

2 flat Ability power Quintessences; Need Base damage somewhere
1 Attack Speed Quintessence; More Attack Speed!!!!!!

You want sheen instantly there's nothing like watching a Champ run from you after he sees 1/3 of his health vanish from just one melee attack with Nether Blade + Sheen proc.
Obviously you are still Squishy with roughly 1.8k hp at 18 however if you feel Rabandon's isnt the right item You could alternate in a Warmogs or something with some more defense that suites your liking.
Why Ionic Spark? You could alternate it with a Sword of the Divine, More attack Speed, but the Chain lightning is exceptional if you push minions to the next capture node, also the 250 health does help somewhat with your low health pool situation.

Start off with a Point in each get a Force pulse ready before the gates open!
Also can try 1 Nether Blade and 2 Force pulse Get Void Sphere on level 4 depending if your going defensive or assaulting windmill.

I Just Took my 2 favorite Summoner Spells and they have never failed on any champ i play, other decent Spells to try are
Flash
Cleanse
Or either of the 2 new Dominion Spells if no one else on your team will pick them up.

Starting off your obviously going to be slower than most people, everyone always seems to grab boots and race to Windmill so don't ever chase until level 6.

Early Game all your abilities will be useful and will pack a decent damage, MAKE SURE YOU SPREAD YOUR ABILITIES OUT SO YOU CAN MAX OUT YOUR SHEEN DAMAGE! Think of Riven's play Style.

By Mid game your Null Sphere and Force pulse will inflict little damage and should be used either to slow/Silence or most importantly Activate Sheen.

Late Game all your Abilities will be useful and damaging again. You should feel almost like a Yii, only with Nukes and disables.

With the Fast play style you should try and capture middle buff whenever it's up, it adds a double does of ionic spark to your arsenal!
And remember Kills Aren't the primary objective, that doesn't mean there not important if your can Riftwalk into a group of 3 low heath champs and take them down that's just more time your team and you have an advantage at capturing nodes!