It can be done, but what of the aircraft band radio when you have the antenna switched to the ham rig? That is, what if someone were trying to call you on the aircraft frequencies--especially for an emergency?
The plane has dual GPS/Nav/Comms, both with standby frequencies, so I would only be using the antenna for one of them and would therefore always have the other aircraft radio available. I usually fly by instrument flight rules (IFR) on cross country trips and would have someone (usually my son) monitoring the aircraft radio for frequency changes, etc.
...All in all, it's best that you put a separate antenna for the ham bands on your aircraft....
That is the reason I purchased the Comant CI-292-3. I have operated with a 2 meter antenna installed on the top of the cockpit in an Archer and a TSO'd business band VHF antenna installed on the top of the wing on a Maule. I was really wanting to try a belly mount antenna on the Mooney.
Another detail is that I have the Mooney for sale to trade for a helicopter. I have several trips planned that I will continue to make in the Mooney until it sells. I think it is worth going to the trouble of connecting into one of the aircraft antennas, even with some loss, without making any permanent modifications to the plane. The blade type aircraft antennas that I have now are known to be broadbanded. I am thinking that the match will not actually be that bad. I am hoping that someone has tried this.