You might take a look around for an ankle style holder. I have a friend at work that carries his back-up on one ankle and spare mags on the other, in a carrier.
I'll play the part of oddball. I only occasionally carry a spare since the vast majority of the scenarios I can imagine will resolve one way or the other without reloading. Yeah, I'll be sorry when the zombie apocalypse begins, but other than that, I don't anticipate a protracted gun fight.