We have recently marked down a group of products and do NOT want to mark them down any further. We have some customers that have a pricing level with a certain percentage marked off. Is it possible to exclude these "closeout" products from that percentage off (besides adding all the items to the customer item pricing list)?

I don´t think so. I would say you need to add those to the customer item pricing list. But if you find a way to do it let me know, I am interested in if there is an out of the box solution.

I did end up going a different way. Since we are closing out these items (and don't intend to sell them any more after they are sold out), I simply marked the base price (and subsequent discount prices) to null. This translated over to the website perfectly.