I tend to agree with Martin on this one for the most part .... but down the road, if you wish to allow a handful of your best affiliates the ability to bring on strong affiliates, one at a time ... through a tracking link so you know that the referrals are theirs ... I see no reason why you'd run into a problem tallying up their performance seperately and paying them manually through PP without categorizing it as a 2nd tier commission (if this is a problem, you could always cut a check).
The only reason I say this is that ... as a broker, I've done what I call a 'golden pass' time period where JV partners were given a short window of opportunity to bring on a limited number of close associates in return for a second tier per referred sale ... now, of course, if there is a limited time and number ... affiliates almost always bring on their most productive partners ... this has some times doubled partners in a very short period of time, and although additional money is paid out on the extra tier, the volume easily makes up for it ... not to mention acquiring new partners we may not have had access to (or even heard of).
I'm assuming you'll be using a CB affiliate management system?