Hiya Toni,
If you include PayPal subscription buttons on the pages, they can do it that way. I'm pretty sure PayPal has the ability to create buttons for that type of thing, I'm not 100% positive, but I think so. Let us know if that works for you or if they have it or not so we know that too. They have soooo many different buttons that you can create right on the Paypal site and get the code for that it would stand to reason that a subscription button would be there too. Take a look there and see.
Once you have that code you can include it on the pages that you "don't" have protected. Put a nice explanation on the page to let them know that this is not an immediate process and that the subscription will be activated within X number of minutes/hours/days or whatever. From there you can setup an account for them in WAM and send them the password via email (making sure of course that they include their email in the subscription information they send with the PayPal button).
I can see no reason why that would not work. Not as handy as automated setup and immediate gratification for the customer, but it definitely should work pretty slick. Good luck with it however you decide to go