All I know is if you go to my Ebay then click on Preferences under my Account then Go to buyer requirements and click on edit then under that is: Buyer Block Exemption List down towards the bottom of the page is: Add a Buyer to My Exemption List.
I don't know if that will work. If you set up a block list for low feedback buyers then you would need to go and add them to this "Buyer Block Exemption List" for them to bid on auctions.
Most sellers will not run into this because ebay has their CC # already.