This might be asking for a completely different hack, but would it be possible to make this work the opposite way with usernames/passwords also?
Through this the registration process can be deleted if you want only your registered members to have access to the UBB without entering each one manually. The username, password, and info combinations can be pulled from another file rather than (and/or in addition to) only having people sign up to the UBB through the UBB registration process.