Supporters or Upgrades or ???

I love the idea of the supporter plugin, but I’m not sure if it is the best tool for my situation. I already have a billing application and merchant account (WHMCS/QuantumGateway) that I use for various recurring transactions, so I don’t want to complicate things by adding PayPal to the mix. Nor do I intend to show ads on the front end anytime soon (maybe someday on abandoned blogs where the admin hasn’t logged in for 180 days or some such).

What I’d really like is to take the order on my existing billing system, then manually toggle an upgraded feature set (i.e. expanded quota and plugin access) on/off to the appropriate blog. If I understand correctly, with Supporters, I can currently “extend” a blog's Supporter status for up to 365 days. But, can I easily modify the extend to have an option for 99999 days or whatever then “extend” them to 0 days if they no longer wish pay for the options (and also avoid having to manually extend each supporter every 365 days)?

I guess I’m not clear if Supporter is the best tool for my situation. Maybe Upgrades is a better fit or possibly even Plugin Commander?

I’d appreciate advice from those who are familiar with the packages.