How can I apply day pass payments to membership purchases?

[TSF3725]

I have a Childrens Museum who sells Day Passes @ $8 for residents and $10 for non-residents. At the end of the day, the person who purchased the Day Pass wants to purchase a Membership and have his Day Pass payment be applied to the Membership.  I tried Discounts but I can't seem to get it to reduce the day pass purchase.  It is being imported to Quickbooks incorrectly.  I want to set it up so when I import my sales, the Day Pass sales are reduced and the Memberships sales are increased (not a net amount with the Day Pass credit included with the Memberships sales).

Any suggestions out there?