Shopper Group Based on Joomla Group

[PromoNet]

Is there a way to base a users shopper group based on what joomla group they are in?

This is the scenario for a site I am working on.

There are multiple membership types which I plan on using RS Membership to control. 
RS Membership allows me to assign a specific joomla user group based on membership type.

So all I need to do now is tie the 2 together to create discounts based on which joomla group the user is in.

I've looked round for plugins but I can't find anything.