One potential problem is that aftertouch is active across the entire keyboard, even if it is doing something to only one zone, so as you play perhaps a little heavier on the left hand, whether you like it or not, it's going to pitch up the right hand notes a little (or a lot!). I really like aftertouch for vibratos (especially if you can adjust rate as well as depth with aftertouch) but have never managed to successfully ACCURATELY bend solos with AT.

If you absolutely can't take your left hand off the keyboard to use the pitch lever, the footpedal is probably your best bet, BUT........... (and I don't know of anyone that makes one) you REALLY need to have it spring back to fully up when you take your foot off it, or your part(s) will end up out of tune!!

Anyone out there ever come across a spring loaded Controller pedal??