I tried once using a cable with a normal jackstick (like the one on the headset) and a mini-jack in the other end to go in the camcorder. No engine noise, however, there was an irritating high pitch tone that changed with the prop revs. I guess this is because of the difference in the output of the intercom and the input of the cam mic that you mentioned?
Please post if you find solution as I'm interested to know as well - thanks.