Given the opportunity to do it properly, I would split the cases and replace the seal.
On the other hand, if I was being lazy and was working on an engine that I didn't care if I lossed, then I might try pushing it in there. I definitely feel that this should only be tried by someone who knows what they are doing.....
There is alot of things that could potentially go wrong there when customizing the PTO seal and bonding it in. It's one of those things, that could cause a not-so-apparent problem later.....