Could definitely do that too. I also thought about the Dawn of the Dead remake, but it might have a few too many kernels of humor in it and throw a wrench in attempts to riff it (it deserves it, though).
Probably the way I'd go about riffing is the same they they wrote jokes for MST - watch it a few times, write down good jokes and the time they correspond to, then compile them together and record a riff.