Is it possible to allow free blog and premium blogs choice at signup


I am testing out the Pro Sites plugin, and I would like to know if it is possible to offer a choice between users/visitors just signing up to a normal free site or purchasing a paid blog on the front end?
i.e. Giving people two options upfront, instead of only a free blog at the start OR a premium one.

If this ability is not included in the standard setup of the plugin, thats fine, however I am not sure if it is or not?

If it isn't can this please be submitted as a feature request...