Since the customers could be using any one of thousands of different credit card companies, each with its own rules about how they capture transactions, I'm not sure this is practical.

I bet this is possible.  I would speak with your reseller, I'm thinking that they could change the comment that SPS gets and that 'might' get passed all the way to the end user CC statement (or the Master Developer they hire).  Doug could be right though.  And if I'm correct then it's probably not inexpensive to have this done (via a customization I'd think).

Note that Doug's company is a master developer and a good one so ... I'd check anyway.