Forget the cup....that is a mug's way of fixing issues and you are going to end up with rot and mold if you pursue that course. Hopefully you were just trying to be funny, I was certainly amused by it
If you must do a quick fix use some Captain
Tolleys, you are likely to need 5 or 6 applications of the Captain
Tulleys for to find its way in to seal up the void. Follow the application directions.
But truthfully you should do the job right, take the windows
out, rehabilitate them and then reinstall using new seals to replace any old ones that have started to deteriorate.