Hi Tony,
I've not heard of that, but I guess it would be possible if you had the technical skill.
Not quite the same, but what I did:
* connected a standard external speaker to the radio (PRC-10) - it looks like normal.
* I took the back off the speaker, fed two black wires in through the cable hole and then connected these to the +/- respectively. Replaced the cover.
* The other end of the two wires has a headphone jack. I connect it to a small MP3 player that sits in a golf bag. I tuck the wire away so you can't readily see it.
The MP3 player has live recordings of 7 RAR and 1 Armd Regt in combat in Sth Vietnam.... through the tinnie speaker, it sounds as real as it gets.
Pete