Bananas are quite irritating by themselves, even without the glycerine. But riper ones are more irritating (more sugar). To get these in you need a really relaxed anus, so do whatever it takes to get there. A succession of bigger toys will do it nicely. Then break in half and stick the pointy end up your well lubricated bum. The first few halves go in really easily, but then you have to push a little harder, or perhaps shove a big toy in on top of what's already in your rectum. The idea is to force the rectum's contents into the descending colon. Once this process has begun, the passage seems to say open, and you can shove many more up. Some will squish and there will be a bit of a mess, but it is only banana, after all!
My limit is about 24 average bananas (only if the descending colon is empty), and I assure you that you will not be able to hold that many ripe onesfor more than a few minutes.