It's easier than that - use two blocks of different repetition frequencies (which gives two different Nyquist velocities), get two velocity readings. Some basic number theory will get you the right answer.
Using two different carriers is going to alter the Nyquist velocity by such a small amount that it's not worth doing. Unless the carriers are very widely separated (go from say, 2.7 GHz to 5.8 GHz) but this requires a wideband (and necessarily low gain) antenna.
That's not to say that FHSS is not used by weather radar - its purpose is to improve the quality of measurements by increasing the number of statistically independent samples that get averaged together.