Any chance you could take him to a vet? Or perhaps set up for a mini chicken surgery to try and remove it? (Surgery stuff just in case it bleeds or something!) I'm insanely curious, I didn't think Echidnas could stick their quills in things like a porcupine, and I also don't think they're...
Porcupine quill? Those don't live where I live so I've never seen one, I'm entirely unfamiliar, but they are hooked/barbed so maybe that's why it's not coming out? I'm clueless :0