I am currently converting a very old, but working classic ASP site to ASP.Net.
It has a completely custom written user management system. Whilst it work
That video does complicate things :) If you're going to implement a custom provider then reflector over the existing one is a good place to start :)
As a quick and dirty option you could, of course, hack the stored procedures that the SQL Membership provider uses but the custom code to provision services is probably stretching that.
If you think about it the remote provisioning of services doesn't really belong in a membership provider, it's not really a membership function - all membership does is provide usernames and passwords and authentication around them. My own feeling is that you should move the provisioning of services out of there, and perform it on the ASP.NET site after a user has been created - even if that's just calling a stored procedure once the membership provider has done its thing. If you do this you may find that the SQL membership provider will do everything you need it to (probably with the Roles & profile providers too), and thus you have way less code to write!