Well the simplest approach would be to buy a set of normally open (no magnet present no conduction) Security switches from like radio shack.
Not the best sizing but....
When the magnet is close to the switch it closes the contacts.
Snip there PTT switch off and wire this new one in.
Incorporate it into your gloves. Put the magnet on the steering wheel someplace where your finger can reach it to choose PTT.
Or if you have an older bicycle electronic odometer it uses the same
technology. There much smaller than the security switches.
Our digitron pickups I beleive are inductive and not a reed switch.
I have several reed switches. But they are glass tubes. Tiny and fragile.
I would also add a magnet to the back side of your other hand's glove.
So if your out of the Pilot but want to transmit you won't have to reach for the wheel just touch the other glove with your trigger finger. Assuming the radio and all is on your buddy and the helmet is on.
If you can't find this stuff let me know. I have a bicycle odometer pickup switch laying around someplace. maybe I can slip it into the UPS package bouncing through my address.
A hall affect sensor does the same sort of thing and is like a transistor
and much more durable than a reed switch. However would require a bit of circuitry. An old harddrive can harvest around 4 or 8 hall affect sensors. There used to monitor and control the spindle rotation.
I would use these when I get around to building a drive vs driven clutch monitor/measurement sensor.
Both of which are sensitive to magnetic polarity just FYI.