We are implementing an online membership for a gun club using CBSubs. Currently, all of their members have paid offline by check. New (gunclub) members who register on the site will be asked to pay a $100/yr membership fee, however existing club members need to be able to go signup at the website and create their profile without being charged the $100 fee.

My first attempt was to set up a promotion with a code like "PAID2011" and have that code give a 100% discount on the subscription fee, but it just sends the customer to paypal with a $0.00 balance and then paypal says you can't have a zero balance and the process stalls.

Any suggestions for a more elegant way to accomplish this?