Cool, I agree with what the others said about switching to Seroquel, and remember that Seroquel is typically more sedating at lower doses. For me at least, it works fast so maybe try the 200 for a couple days and call your pdoc to adjust the dosage or at least get enough to take 300mg. If you really want to, you can give yourself a slower taper off Zyprexa by cutting the pills into halfs/quarters (depending on how you get the 7.5),and 7.5 isn't that high of a dose for zyprexa, I remember being on 30mg at one point.
Try it out. I wouldn't worry that much about insomnia especially just starting Seroquel.