market press pro sites

I'd like to make it so that non-admin users can pay for the pro version of someone else's site.
If you want another user to upgrade a user, in pro sites activate "Bulk Upgrades" module

do_action('psts_upgrade', $blog_id, $level, $old_level);

how might be the best way to do this modification to the market press plugin? i assume i would create my own plugin folder with the code there, right? what action would i look for from Market Press?