wp-signup page without theme

Hi
I am trying to use a theme from yootheme on this test site.
http://mediasentrum.com/test/wp-air

Problem is that theme is not displayed on signup.php page.
http://mediasentrum.com/test/wp-air/wp-signup.php

Theme developer is not willing to provide any help with that and just says that multisite is not supported at this time. But I think it might be a little thing I must add to display the theme correctly on signup page.

Can anybody help me here?