Thanks for the comments. I don't really care much how we do it as long as we get the darn flagman out of the picture.

I would say that having attended a couple contests where Barb Smith was the radio controller, that works well by my observation. Her duty cycle on the radio was certainly less than 1% so I don't think there was an impact to safety calls on the radio. With respect to the example case of interfering with a safety call from a glider to it's own tug, there wouldn't really be interference. That because the radio signal power from a glider 200 feet away will not be impaired by the signal from a handheld which is a mile or more distant; it's a 1/r^2 matter, the close radio wins. Aircraft radios use simple amplitude modulation.