Can you split user registration from site creation

Not sure if this is possible without hacking. We have a main site with BuddyPress social features, and people can also register their own sites (multisite & Pro Sites & New Blog Templates).

At the moment the site Register link always has user registration plus site creation including all the New Blog Templates. It's too easy to enter some details incorrectly. Also puts people off as it's more complicated than necessary for users to register just for the BuddyPress site.

Is there a non-hacking way to have Register as only user registration, then the user can use the Create a site button to create a site when already logged in?