Similar to http://wordpress.org/plugins/buddypress-virtual-gifts-widget-make-money-boost-social-network-engagement/ but not giving the developer a piece of the pie. Users can expend their own points from Q&A and other plugins that reward points for comments, likes, etc.
Of course, a user class say developers could purchase a block of points to spend on our mutual cutomers for a gift icon to their profile?
Discus with the dev who made the whmcs integration about profile syncing to whmcs tblclients and API that creates the invoice to pay.
If the user level is lower, they only can expend points from their activity on the site.