That's looks quite tricky. The problem is that the wishlist needs the posted ContentObjectID and ezOption to add the product to the wishlist. And if you are redirected to the login page, the post data is lost.
A possible approach might be to hack the wishlist.php so it works with sessions as well and put the posted data in the session before the wishlist redirects to the login page.
Since you have already managed to get redirected back to the wishlist after login, the wishlist should then check for session variables, add the product and remove the session variables.
Maybe you should also just add the redirection to the wishlist if one of these session variables is set - after all you don't want to redirect to the wishlist every time someone logs in.