Wow.. I got it to work.
Placed a B2G1 order for Prince of Persia, Crackdown 2, and Darksiders (all of 360) - Came out under $10
Then placed and order using the B2G2, for Uncharted 3, Saints Row 3, R&C - A Crack in Time, and Dark Souls, using $15 in reward zone certs. So ended up spending ~$30 in trade credit.
The B2G1 is for shipping, and the only game shipping out of the B2G2 is R&C (not one of the free ones). The other 3 were available for in-store pickup.
Thanks!