GF User Registration + WPMU Pro Site Level selection

Hi all,
I am currently using the User registration add-on for my multisite signup. And using WPMU's Pro Sites to create different levels of membership.

Does any one know of a way to enable a user to select a Pro site level on signup instead of using the default that you set in the Pro Site settings.

I.E. Please select which membership type you would like.
Free - Bronze - Silver - Gold

The following post touches on it but its wanting to integrate a different feature so though I'd ask. http://www.gravityhelp.com/forums/topic/creating-new-sites-in-a-network-after-taking-payment

I've asked over at the WPMU forums and they have suggested looking at the extend function and get GF to trigger it, but honestly I am at a loss.

Here's the function
function extend($blog_id, $extend, $gateway = false, $level = 1, $amount = false)

I'm going through the docs and think this http://www.gravityhelp.com/documentation/page/Gform_user_registration_add_option_section may help, but if anyone can steer me in the right direction that would be great.

Thanks in advance,
D

Cheers Hiranthi,
I'll let you know how it all goes.
D