Chose a Usergroup after Subscription 3.6

[CouchMonkey]

I know this has been brought up before, but I havent seen any solutions that would resolve my problem.

I am looking for a hack to basically facilitate movement into a peticular usergroup after they paid a subscription fee.

For example:

User signs up and subscribes for 1 month of service. After the transaction is complete, I would like them to be presented with a choice of usergroups. The user makes the choice and is put into that usergroup. The user is not able to chose a different usergroup until their subscription is up.

Is there a hack out there that can do this?

If not, i would like to request one. I will pay if done correctly. Please feel free to PM for more details.

Thanks in advance!