There are Bluetooth audio transmitters made to plug into smartphones and digital audio players. I have no idea how good any of them are in terms of audio quality, latency, weight, or pairing.
Latency, I don't care about, since it's mainly music that's interesting. But I'll have to look into those (particularly if anyone on the forum has actually tried one and liked it! cough cough
I realize that a stereo plug does not provide sufficient energy for a wireless device, but I was hoping, maybe, there was something amplified by a mere button-cell... it's not just the torque, but also the risk of my dog walking across the cable and ripping it out, or whatever. He likes to snuggle at my feet, which tend to be in a direct line between my chair and my speakers.