user role issue

Hi there i am having trouble working out the best way to go about doing something.I have a plugin running that allows me to create vendor stores where clients can have there own products on my store.
I also have your affiliate plugin running. I want all vendor store clients to also have an affiliate account, but not all affiliate clients will be vendor clients.
I have tried a plugin to assign the affiliate plugin capabilities to the vendor store plugin user role and used your short code to put your affiliate client page stuff onto the vendor store client admin page. but when going to the page the affiliate content on the page is not visible because it wants the client to register. but of course if client clicks the link and fills in the form they will get the that email already exists because they used it when creating the vendor account.
I know this is not a problem with your plugin but just wondered if you know of anyway to achieve what im trying to do