Dropdown for a product proof

[MAshin]

I have a product that be customized and have added a dropdown for Proof (yes/no, where yes adds $5). The product also has quantity pricing enabled, 1 is $10, 2 are $18, 4 are $32, etc. When I add qty 1 and a proof, the shopping cart correctly displays $15, but when I add qty of 4, the shopping cart charges for 4 proofs plus $32. I only want the proof charge to go through once in that case. Any idea of how to do that?

[dortchjm]

List the proof and product as subproducts.

Janice