Looking at the picture of the EBay item a little closer, and reading some of the reviews, it seems that the pump nozzle has a groove on it, that is exposed when you push back the rubber booty. The hole in the card is not a straight slot, but rather it looks like the slot is larger on one side. It seems like the slot allows you to slip it over the pump nozzle, and then slide the card to the side and hook the smaller radiused side onto the groove on the pump nozzle.
It looks like I need to bring some calipers with me, and take some measurements of the pump nozzle. I have some marine grade plastic in my shop. I can make a card to match the EBay one easily.
seriously, just use your free hand and hold the seal part back - - you dont need to make or carry some special tool to do this