Affiliate for WooCommerce

We’d like a setting which lets us toggle the following functionality:
Choose which visitors are eligible as a referred visitor:
– Everyone
– Only visitors who haven’t made a purchase before
– Only new visitors

What this setting could do:
Give you the option to choose if existing customers can still be “claimed” (at a loss for a better word) by an Affiliate, or only the customers who actually found your site by the affiliate link. We wouldn’t want an existing customer of ours find out that if they press an affiliate link, which basically makes us pay twice for both the affiliate and the customer we already had.