Customer Survey Coupon Not Working for Games?

I recently completed the Stardock Customer Survey and received a coupon code for a single purchase.  The document notes that it is restricted to sales on the Stardock customer site and includes a link to shop for games.  However, for every game that I tried, either I get redirected to the Steam Store (where the coupon obviously won't work) or I end up in the FastSpring checkout.  For games (unlike Business software) the FastSpring checkout does not provide an option to add a promotional code (become Coupon code when clicked for business software).  The game I wanted to purchase was Star Control: Origins but the problem seems to apply to other games as well.  Is this related to the fact that Stardock has chosen to fulfill the game installation via Steam?

I am annoyed that Stardock is not honoring the coupon for games purchases.  I won't be making a purchase until this is resolved.