My moto is, if it can have bluetooth, it should. So let me introduce you with my latest mod, the wireless ISK HF2010!
The bluetooth module was salvaged from an in ear QCY QY8, including the tiny battery which i will probably replace with a larger one later. Not the cleanest build, but better than i expected. One caveat is i can now not control the volume from the headphones, and there is no visible indicator light, but i can live with these, after all this project was mostly for fun, but im actually quite satisfied with the outcome.