I think I found the answer on the irrigationtutorials.com. The solution is to use different nozzles to match the gpm based on the angle coverage. E.g. use a 1gpm for the 1/4 circle, 2gpm for the 1/2, 4gpm for the full circle.
But this raises a second question. When you use different nozzles, you also change the radius. If I'm using a nozzle 4 times larger than the radius I need for the full heads, it would seem I need to cut the radius by nearly half. Does that cause any problems? Doesn't that significantly affect the distribution profile? Also, I'm looking at the Hunter PGJ and their brochure says that the radius adjustment screw can reduce the radius by up to 25% which isn't enough to get the 4gpm nozzle down to the radius of the 1gpm. So is it just impossible to mix 1/4 and full head rotors with the PGJ? Are there other small-radius rotors that don't have this problem?