There are stick on card holders to fit on the back of your phone that should fit on the Swiss Card as well.
I know this probably ain't the answer you're looking for, but I'd make one out of leather and clear plastic. One piece of leather would have the plastic glued on for ID visibility, and the the other would hold the SwissCard. Between those two would be a third piece, slightly taller, with a hole for the neck lanyard's hook.