You can do it with a serial cable but you are getting into a big job. The ideal way to do it is to have two head units so you can use the connectors from the body and face of one. Of course this is assuming we are talking about a detachable face radio. But all you have to do is lengthen the connection of the faceplate to the body. Just solder the wire from the serial cable to thematching conncter and you are done. If you can't afford another radio for parts(which, if so, shouldn't really be attempting this anyway), You have to create a way to connect each wire to the connection without dripping solder and creating a bridge between two connections which would in turn cause you to have to buy another radio anyway.