Force Coupon Use

I'd like to force the user to input a coupon code on certain promotional products in order to get it free. But since I have to show a value in order to have a 100% discount, the user will be sent to PayPal if they forget to input the coupon code. We would rather avoid customer service issues and just force them to input a coupon code on those products.

Any thoughts?

You could run a javascript check upon the submitting of the signup form.

After some more searching I found the answer here - http://www.amember.com/forum/showthread.php?t=5919