If what you want is just the communications why even start the beast up? If for some reason you need to be flying at the time you will need to patch into the com lines, maybe with something in the link above.
If you go that route make sure they know and are fine with it. You don't want to screw up the communications while you are in flight.
Also you may need to get permission from everyone who says anything. It really depends on the state but many require permission from everyone on a "tapped" line and that is essentially what you will be doing. Even ones that only require one persons permission, that one person needs to be a participant in the conversation, which you probably won't be.
How about something like this: It is made for phone conversations, it is an ear bud with a mic on it. I have one and it works pretty well, you could simply wear it under the head set and cable it to your recorder.
Of course all the other permissions and cautions still apply.