Canon wireless flash is all infared based so line of sight between trigger and unit will always be required. I little short sighted I've always thought as you will want the offboard unit hidden, or facaing away more often than not.
I've been thinking about getting something to be able to run a little group of speedlights off the camera when the power of studio heads isn't required but haven't looked into it yet.
I'm hoping that there might be some little slave units that will sit on the hotshoe connection and be the trigger, as that would work just as well for me as radio units and be much cheaper.