I decided to write my own plugin for it, which I have just submitted to the wordpress.org plugin repository. It still needs to be approved for publication on the site, but you can already download it here.
The plugin lets your signed up members send traffic to any page on your wordpress site, appending ?affid=username to the end of the url (replacing username with their own username on your site) If someone registers on your site, the referring member will get credit for the new member. The plugin also lets you specify a page you want people to be send to after logging in (instead of the wordpress admin panel)
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