I know this doesn't answer your exact question...
But my Lightspeed PFX have the bluetooth recording functionality thing. I've used it a couple of times to record to the iPhone / iPad then transfer that and dub it over the top of the video. A couple of times I've had glitches though where it's recorded me and not the ATC or just recorded nothing at all.
I was looking at those cable thingies that plug in to the audio jack in the plane then directly into the USB socket in the gopro (Nflightcam or something), but I don't know how that would affect the usual ambient noise. Plus it's £40 for a bit of wire.
I may just end up doing what this fella does.
https://www.youtube.com/watch?v=kbyclqtP46A