That's a lot of credit. It's the only way I found to work. Getting a CSR to subtract the $5 from the price would work, except you wouldn't see a drop on the movie until it drops below $26.99 with the $5 adjustment. Whereas if the movie drops to $24.99 with the coupon, you'd pay $19.99. It...
Pre-order something else to use the gift card balance and then place a second order for the movie with the coupon. Then cancel your first order that you used the gift card on and you'll still have it.