Unfortunately most spices are a no no for me. They seem to aggrevate my gut. That said I haven't specifically tried cayenne pepper, but I have tried cumin, paprika and chili powder without favourable results.
I do have a fibre supplement although am unsure on the dosage. They are 440mg tablets, of which you take 2 before you main meals. I guess I'd be safe to ease up to 6 or so of these a day.