Ah yes, gastrointestinal cramps. I've struggled with IBS problems for years, and they only get worse when bent over a bicycle.

Things that have helped:
1. Avoiding high-rise and/or too tight waistbands on cycling clothing. The ultimate in belly-comfort is a bib-style short, which... well... isn't for everyone. I have had good results with just being a selective shopper and finding shorts/tights that fit me well and have scooped waists in front.

2. Work on your GI/health issues. If your stomach is generally unhappy all of the time, there's a bigger problem you should work on. In my case, eventually I learned that dairy, wheat, and soy all aggravate my tract and the pain is simply not worth it. When I'm being good on my diet I am generally free of all discomfort, something I never would have believed 5 years ago.