The best I can think of is having assistance to the washroom. I don't know how you would manage that.. I had an ostomy on a 6hr flight and I had to empty (a lot. I had the stomach flu) and no one complained about a smell. I also didn't have to change my bag on the plane though. I recommend putting a new bag on shorty before you go on your trip.. That always helps me (I'm prone to leaks).
I wish I could be more helpful! I'm sorry.
Check with your health insurance about coverage for a "flight nurse." That's an RN that your insurance pays to meet you at the airport and fly with you. They do many types of skilled nursing tasks such as monitoring feeding pumps, running IVs, administering medication, etc. It's *possible* that they also can do toileting care, which in your case would be bag changes and/or assisting with transfers. If your personal health insurance does not cover flight nursing, you can also look into your options for travel insurance. I know one of my relatives had a flight nurse covered by travel insurance to accompany her in travel home from overseas after her release from that country's hospital with a badly broken leg.
The only other thing that I can think of is to discuss the issue with your physician. It's unlikely, but I suppose possible, that they might have an idea for something that would either "clear you out" like they do for colonoscopy before the flight so you'd have minimal if any stool output or (perhaps more likely?) could give you something to constipate you intentionally just for 12-24 hours. I know when I had a fecal microbiota transplant, the hospital gave me something to stay constipated for 24 hours so I wouldn't "lose" my transplant before it "took." I can't say whether they would be willing to do something of that nature for travel purposes or not for sure, but it never hurts to ask your doctor/surgeon's advice!
Thanks for your very thoughtful suggestions. I think that I'm moving towards a solution for a long flight. Slowing down the digestion was suggested by my gastric surgeon, also I've heard of extensions which can be added to a standard bag - sort of long range tanks! In my neck of the woods, travelling with an RN can be tax deductible. No harm in trying the health insurance folk although if it was a holiday trip I don't think they would be interested!