Adult Check used to require that you got 1 sale before activating your free pass that worked on all their sites.
Busty Amateurs offered access to their members area but I believe they required you to send them the url to one of your sites first that had a BA banner and your referral code on it.
You can also ask webmasters to e-mail your from an adult site e-mail address like
[email protected]. If some one e-mails me from
[email protected] and asks for a password I tell them to e-mail me from a real address first and provide some proof of being a webmaster.