@Capt'n Corrupt: you are giving away your age if you remember those types of remotes, lol. But spot on, I'm envisaging a matchbox sized device with a highly selective audio filter that converts audio pulse train to IR. It would have the advantage of being cheap and not requiring additional hw (such as some BT/networked device). All assuming the RC codes can be captured or dl'ed somewhere. I am not an audio engineer though and suspect some specialist equipment is needed to test if this idea would be feasible.
Ah, early remotes.. I remember those. They used ultrasound. That didn't last long, because the ultrasound sometimes went through the walls and when you had just sat down to watch "Flipper" (which was popular back then.. your TV would switch channels because the neighbour operated his own ultrasound remote.