One of the claims of those brakes is that since they are a closed system they do not need to be bled ever. So I would assume there is no procedure to bleed them, it may not be possible.
It could be sticky pistons. I recently took my Ultegra brakes off, removed the pads, and tri-flowed the snot out of the pistons. It was time to change pads anyway, but they retract a lot faster after braking than they did before the tri-flow.
It's not so much that they don't retract. It's that they lock up (pads push up against the disc, as if I was holding down the lever) under heavy braking (presumably from the heat). It also becomes harder to squeeze the lever to get the same amount of braking power when this happens. They'll return to normal after a few minutes of cooling.
I used to have those brakes. While I'm not sure it will solve your problem, they can be bled (I had my LBS do it). The reason I needed that was because mine came from the factory with too much brake fluid in them (at least, that was the LBS's diagnosis), and the pistons just wouldn't retract enough to clear the rotors.
