We knock him down with 2 sorcerers (sages) about 3-5 seconds after he starts channeling every time we kill him. It's all about actually moving him to a proper spot before you start, and it will be no problem no matter what classes you bring.
Yes, you both have a force stomp that would make it easy. My comp did not.
Composition for a flashpoint should not matters as long as you have H/T/D/D
Also, I meant the person tanking was a vanguard, not commando.