Your "feeling" is correct.

If you do a search on "carb blockers", you'll probably find a lot of threads on the subject. I'm sure that if they worked, pharmecutical companies would be pumping them out like crazy and they'd be selling like hot cakes. If anything, they seem to just cause upset stomachs. I think you'd be better off just taking a fiber supplement before your "off plan" moments to curb the "damage".