Gravity Forms & Multi Domains

Hey again,
Sorry its about the same issue I am having. I thought I should start again because I might not have made much sense before....

So in the simplest form possible this what I want to do:

I want add another domain to my network through the multi domain plugin, and then I want users to be able to create a site under the added domain via a Gravity Forms User Register Form (essentially just another 'register' form).

How do I do this?

Note: Currently the GF form will only register sites under the main network domain.

Cheers

Nimruzir