Marketpress customer logins


I have Marketpress set up not requiring login.

When a user checks out there are at least two places where they can (optionally) login, so they can track their orders.

Both these places (classes mp_cart_login_link and the form in the class mp_cart_login) fire off to wp-login.php

Which is all fair enough, except that is the default login page for my multi-site, so when they register they are given the option to add a new site (well worse for me, as I have customised registration, assuming everyone wants a site)

Is there a way to ‘hook’ in a custom login page specifically for these market press links (as I would want to not allow site creation from that custom page and make the ‘register’ link a bigger button)

Advice how to achieve this gratefully received.