programmatically setting a level

is there a call i can add to the pro-site system so when some one signs up for there own site i can set them to a different level. all site owners would have the same membership level.

what i am thinking is to change the PHP in the create site and add this call so any one that creates a site is set to this membership level.

I got this idea from one of the threads but know i can not find the thread.