Adding a headphone jack to stock stereo

[Gonfast38]

I just bought an '06 Road Glide and it doesn't have CB or anything beyond the standard stereo. I have a Nolan Ncom helmet and I want to listen to the stereo in the helmet. I asked my local dealer and they say I have to add the CB module and all the associated parts to the tune of around $400. Thats getting a bit pricey. I don't need the cb or anything else. I have moderate skills with wiring and can read a schematic. It looks as if I can just add a couple wires to the radio modular connector and add in my own jack in the dash. Has anyone done anything like this? That radio looks real expensive and I don't want to trash it. Any suggestions?