Can I change affiliate links to usernames ie: www.website.com/user?

I have a client that has an online shop, with local reps that deliver in their own areas. I am re-doing her site, and considering using the Affiliates plugin to manage that. She currently has them under subdomains. It's very important to ensure the inventory of the individual products are centrally managed, and that we don't end up creating an entire separate site for each rep.

My main question is this: I see on the Affiliates page that it creates affiliate urls like: http://www.wpmudev.org?ref=pollyplummer-4314, and I want to know if I can create affiliate urls like: http://www.website.com/pollyplummer.

Does anyone know if this is possible? I can't see it anywhere in the documentation, though I may not have looked where I needed to look.

Thanks in advance!