Paypal Pro Free Sign up form set question!

hello there,
I have set up a free registration form and S-2 member to capture the registration details of a user in order to set up a user without going to PayPal. I’m using the form short code on one of my pages. The reason I’m doing this is because I’m using another plug-in that I customize to allow 100% free coupon codes with S-2 member. Space

my question is regarding the page URL that displays on the URL bar of the browser window. The coupon plug-in that I’m using redirects the user to the page where the PayPal Pro free sign-up form is present. As you can imagine the URL of this page where the pro-free sign-up form is present is fully visible and accessible to anyone who can exploit the site by signing up for free.
Is there a way that I can hide or mask this page URL so that the user cannot gain access to this free registration form by typing it into their browser?
Please let me know if there are any easy solutions for this issue?
Thank you and I look forward to hearing back from you.
Marco

Thank you for your inquiry.

I can’t really give you an official way to do this, as I’m unfamiliar with the other addon you’re using, but I might suggest using wp_create_nonce to validate the request to see your Free Registration Pro Form.

See: http://codex.wordpress.org/Function_Reference/wp_create_nonce