I understand your concerns. I don't have Crohn's though have an irritated lining of my bowel and have to be very careful too. The cleanse I did, did not involve colonic irrigation and still worked great for me. I followed the Hulda Clark e cleanse. I did/do however have trouble with the magnesium salts. They can be very irritating to the bowel so you may want to try this magnesium citrate people are talking about - i haven't tried the citrate yet and have managed to grin and bear the salts.
Just do the best you can and see how you go. The cleanses have been really invaluable for me. Good luck!