I think I have finally perfected my method of pulling root riot cubes apart before moving to 4" pots. Is this necessary? Not technically. Should I not be using root riots in the first place? Probably. But instead of finding it inconvenient I actually look forward to it. I start by gently pulling away roots at the bottom of the cube. Then I remove the top "shoulders" of the cube where there are rarely any roots. Then I dig between major feeder roots with my thumb, to start removing material from the center of the cube, because it also tends to have fewer roots. By that time the radial pattern of the roots starts to free up, and then I can gently roll away clumps of coir with my thumb. By the time the raw stump end of the original node is free, I'm done.
This would absolutely not scale to hundreds or thousands of cuttings. It is more manual than dividing.