I'm planning to do this, with a very similar setup.
I have a 7D, and a 450D.
On the 7D, I have a YN622 trigger, which is going to trigger a remote flash, and on top of the YN622 I have an RF602 transmitter (this is going to trigger the remote camera).
The 450D has the RF602 receiver connected to the cable release socket.
So, when I pull the trigger on the 7D, the 7D shutter triggers, the remote flash is fired, and the remote camera is fired, getting two lit angles.
While I haven't rigged this up yet (only just received the 622's yesterday) it should work fine in practice and other people have reported no issues with this.
So, it's really all about triggers. An rf602/603 pair is all you need - put the transmitter on the hotshoe of your handheld camera, and the receiver plugged into the cable release on the remote camera, and firing the main camera will also fire the remote.