If it is a stand alone THC, then i believe that function will not work. That function should be included in the unit. if its not then....
hmmm maybe a brain would be the answer...
maybe you could have a solid state relay that interrupts the step output line from the pc to the driver, and have a brain look at the feed rate, make a calculation that says that if the feedrate is lower than X open that relay so that the driver doesnt receive the step signal.
or maybe better, have a brain monitor the feedrate, and make calculations not to fall under certain precentage, if it does open the relay.
I dont think there is a way to have mach actually monitor the toolpath to see when you hit a corner, or monitor a g code to see if you hit a g02 g03.
Hope that can get you started.
Regards
Fernando