I use 3/8" and 1/4" SENCO brand staples (@1" long because that's the ones I nomally use in woodwork) as a base to form the correct staples.
You can get them at Home Depot or just about any building supply store.
I cut the legs back to @1/4" or so and insert them and carefully bend the ends over in a slight arch.
I also have 1/4 and 3/8 SENCO staple guns (SLS20 & SKS) and have given some thought to making a backing-block/former to allow me to just shoot them in - but, the idea of shooting one of these things towards my hand on purpose just gives me the

's.
I think I'll stick to shooting them into wood as intended for now ...