What we've done is to replace the links for registration and editing profiles with a link to our customer database application. Then, once the customer has selected their user name, public name, password, etc, that info gets stored in our database and posted back to the right place in the ubb script. I can tell you from the error messages that I can see that it works until it has to write the profile. Then it bombs.
We run conferences, and our users wanted to have their ubb names on their badges too -- the easiest way to do that is for us to have it in the customer db.
Anyway, these are definitely non-standard, but I would think someone must've done something like this before!