We are in the process of removing a previous dba login and he owns all the endpoints and event notification objects. Endpoints were easy to change; Event notification objects not so much.
I found this thread about changing the owner of an event notification object (you have to drop and recreate). I don't want to go through this process again if I can avoid it. I doubt it's possible, but outside of logging in as another user, can you create an event notification that runs as sa, etc.?