The only way to avoid taking chemical bowel prep is to change your diet for a few days to a fasting mode, then give yourself a couple of enemas or go to a professional and get a lengthy colonic. This is drug free, just uses hot water to clean out the colon. But it takes several "washes" to get it clean enough for the prep, so at a professional colonic, you may be on the table for 60 to 90 minutes.
I mixed one bottle of mag citrate, taken the night before, with a professional colonic for about 45 minutes, and I still was not clean enough. But I had only changed my diet for 24 hours though -- if I'd fasted for even 48 hours, I probably would have been clean enough.
I was able to take the magnesium citrate for mine...so I am sure it is possible...just make sure to refrigerate it as it helps get it down...and this does taste better than the other choice and like she said a much smaller amonut : )
Some GI's are now using 3 Dulcolax and a bottle of magnesium citrate for prep.
I don't know of any way to completely clean out the colon sufficiently for a colonoscopy without taking some sort of laxative. Even with the laxatives, they have you on a liquid diet (nothing with red or purple dyes also) for a minimum of 24 hours before teh procedure.
I would definitely talk to your gastro doc about your hypersensitivity to medications and such - maybe they have another suggestion as to how you can adequately prep for the procedure.
The MoviPrep is a LOT of liquid prep, which I would think may increase your chances of having a reaction to it. You may also want to ask your doc about using something such as magnesium citrate (can be purchased over the counter at places like Walmart or pharmacies). It's a much smaller quantity that you drink. They also give this type of laxative in the Fleet Prep kits, usually along with a tablet type of laxative.
Talk to your gastro doc - they can give you more and better advice on what would be safe for you, yet also allow them to do the procedure that they need to do.