I Need an Invitation Code Plugin

I’m running WP 3.0 Multisite + Buddypress 1.2.4 and a slew of other plugins. I’m looking for something that would allow the following scenario:

* Existing member (member A) is auto assigned either a referral URL (http://www.mysite.com/referrals/memberA, maybe) that points to the register page, or a unique referral code (12345).

* Member A posts their unique referral URL or code in thier signatures on other forums, on their Facebook, MySpace, etc., saying “hey everyone, come join this cool site!”

* Referral (member B) sees this and thinks “wow, that looks cool, I think I’ll join”, clicks the link and joins (or goes to mysite.com and enters member A’s referral code when joining).

* Member A gets credit for Member B joining. If possible, it’d be great to have some way of displaying which members are in the lead.

The Secure Invites plugin will keep track of how many signups each member generates, but to refer people, you have to send them an email from an on-site form. I’d like to make it so that sending emails to targets wasn’t necessary. I looked at Pie Register for a few minutes, but it seems that not many have had success with it on 3.0, so I’m scared to even try that (plus I’m not entirely clear that it does what I’m looking for).

Any plugins I’m missing that I should look at?