Upgrades plugin. A few questions.

Hello again

Guys, I started using your Upgrades plugin a while ago.
I'm happy with it so long, but I want to add a few more features (plugins) that users have to pay for.

For example I have a forum plugin from http://simplepressforum.com/ and ecommerce plugin from http://www.instinct.co.nz/e-commerce/
Also I have Donncha's domain mapping plugin.

I want to make these features paid.
So a question - how do I do this?
Is there a piece of code I need to add into each plugin, like for example WPMU plugin filter requires (http://wpmudev.org/project/Wordpress-MU-Plugin-Filter)?
In other words - how do I 'mark' a plugin that I want to make paid and how do I set the amount of credits and 'billing periods' for it?

Thanks in advance.