Ubercart - Product discount based on total number of all products in cart

[glorgo]

I'm using Ubercart in Drupal for a simple web store. I'm having trouble calculating a product discount based on the total number of all products in the cart. For example, I'm easily able to define discounts for if a user buys more than one of the same product, using the uc_custom_price module. But I want to give the discount if they buy more than one of any product. If they buy item 1 for 10 dollars and then add item 2 for 10 dollars, then I want both items to now cost 8 dollars.Hopefully this makes sense. I searched the forums and googled for a couple of hours, but I just can't get this to work correctly. Thanks for your help.