If you want them to do the ppc, mention on your affiliate section that ppc is open and any keywords can be bid on (then theyll all see theres no restricitions on your brand names etc and would be happy to do all the ppc for you for the commission they earn.0
Also you might consider dropping a list of suggested ppc terms (the ones you use already0 if you want them to do it for you
However I can see this being more expensive for you in the long term, and perhaps a dedicated hired ppc specialist? (if such a thing exists) could be hired in to do the ppc for you without having to pay out the huge commissions the affiliates could earn using your ppc.
On a note on
seo, it may take you ages to do but the benefits are worth it in the long haul