I figured out what I was looking for. The answer is to use jit.poke~.
Try this patch out, you can get some strange effects with it. Jitter is easily powerful enough to handle this sort of thing. The 3 rows of knobs correspond to separate 2-op FM synths, one each for the red channel, the green channel, and the blue channel. By turning the knobs you can change what color gets rendered to each pixel. It makes weird video-gamey watery effects. At faster speeds it should be possible to make some very interesting patterns.