Redirect code

OK, this may be custom code so I understand if nobody can help.

On the site, if you are not registered as a "seller" using the membership+ plugin, you cannot post a classified.

Right now when you can click the button "Post a Classified" which links to the visitor protected page of

Since they cannot access that page, it take them to a generic login page. Can I redirect them to the which will allow them to join via the membership plugin?

The page itself it protected under URL /?page=ads
Strip query strings from URL - NO
Regular Expression - NO