Wordpress Multisite & WHMCS Provisioning - Theme & Plugin Activation

How would I go about setting up a wordpress multisite that has the WHMCS integration with WPMU Provisioning plugin and allow certain addons to be WP Themes & Plugins packages? As of now I've got the integration working with the exception that I can only sell a spot on the multisite install and nothing more, I'm curious to see if its possible to further customize or develop a feature to allow themes & plugins to be addons in WHMCS...

Could it be done where a spot on the multisite install could be sold through WHMCS, than the user could have access to theme & plugin access through Pro-sites? This seems to be a tricky approach...

If possible I'd love to know what steps would need to be taken to allow WHMCS to enable/disable certain multisite features and privileges (themes & plugins) through the addons feature.

Thanks!

Phil