Until Live allows time signature changes, you're gonna have to fudge it.
The easiest way for your 4/4 and 3/4 problem is to make the master time sig 12/8. For the 4/4 put the downbeats on 1,4,7,10. For 3/4 the downbeats are 1,5,9.
By the way, you can get some nice polyrhythms going by mixing up 3 ...