This question comes up a lot on other forums. I have never had a security issue with the j-pouch. Let the stewardess//steward know you have a medical condition that makes having immediate access to a bathroom very important. Eat sparingly before and during the flight. Take Immodium every four hours to slow things down. Pack a change of clothing in your carry on. I also pack Calmoseptine for butt burn, Balenol for cleansing, soothing, and lubricating and personal wipes. Only you can judge whether a panty liner or a diaper would be helpful. For me it changes from day to day.
It is one of those events where you may need to keep your sense of humor active to retain a sense of dignity. Sometimes we just have to laugh at the ridiculous things that we have no control over. So far, I have not read a single post from people reporting a bad experience. I hope yours will be another successful flight.