Group Pricing and Paypal Express

I have the following settings on my store:

Zencart v1.5
All products are downloadable
Virtual product
No shipping
Payment option- Only paypal express

I have created a group pricing which has a 100% discount to allow certain members to download items without payment. (They pay after 30 days)

When this happens, I notice that Paypal records a transaction on their report that has $0 transactions on it. So that my report will have a several zero transactions. At one time, I even got charged a transaction fee for a zero transaction.

My question is, should I be adding another payment method on this to prevent the zero transactions on paypal? And if I do add a payment transaction like check, is there a way for it to just appear if the member is under a group pricing of 100% discount?

Thanks