Jarvis: I think so. I was able to do this for Backtrack and Mint on the same USB stick. Although, I didn't extensively test the persistence.
Earbleed: when initrd.gz references casperpath, it tacks on /casper. So if your stick has /boot/bootbt4/casper on it, then the casperpath should be /boot/bootbt4. I believe you also need to have boot=casper on your kernel line