Local auth before pop3

this is where my expertiese falls apart… sry

I guess what im looking for is a hybriduserprovider. I want users to be able to auth on default database, if the user isnt on the default database, then go to pop3, creating the local database user. So the next time they login it would have created them on the default and not passing it to pop3. A surgemail type migriation.