SUPER SOAKER WATER GUN or WATER BALLOONS
Fire off a few rounds or launch a couple balloons just before they pass so they can see what's in store. Preferably requesting a slow pass on channel 16 at the same time. But, as it is with power boaters they usually don't have a VHF radio, at least not on, so 5 loud blasts on an air horn should be enough warning.
And if they don't slow down, let'em fly as they go by.
If they become aggressive after the fact and start to turn around, then get the CG on the horn to let them know what is about to take place.
In my experience nobody cares to hear about people who whine about wakes on the water on the radio. They will care if damage is done, but otherwise it is just another hazard of a dangerous sport.
The other option is to only go out when the price of fuel goes up.