Quoting from a post on another forum -- seems very promising:
"Since I've worked in the Gift Card Processor/Provider field for over a decade, I know of lots of retailers where Credit Cards are not accepted for gift card purchases. In some chains, it varies from store to store. In other retailers, it's programmed into the register as a chain-wide restriction.
First Hand Knowledge Example = I was on a call regarding the launch of a new Prepaid Reloadable Amex at CVS, and American Express representatives ASKED CVS if they were going to restrict the sales to Cash Only. So not only are the credit card companies aware of Cash Only restrictions by major retailers, they have their blessing.
FYI - If anyone cares, the answer was no. So yes, you can use a credit card to reload your Prepaid Amex at CVS (at least for now). Also, Amex is going to announce soon that they are going to waive the load fees from now until the end of the year if you reload at CVS or 7-11."