David,
Since I have an ES with an "RF transparent" fuselage, you can't do it
exactly like I did, but I installed the "E" shaped antenna in my fuselage and
ran it to a jack on my panel. I've never needed it for real, but have tested in
a couple times in flight. It works pretty well, quite a bit better than the
antenna on the radio. So my setup is totally independent of the aircraft
radios.
I agree it's not a good idea to split your antenna signal to a jack that
may never get used. Here's a 2-way switch (photo attached) that could be used
that would allow a full signal in normal operation. I'm not sure how much signal
loss the switch would add.
Mike Easley
Colorado Springs