Why do this at all? Just makes urethane react like a strong, solid cover resin ball. Just throw a resin ball at that point. Plus, the bowler still has to find a line and repeat shots.
The whole ball hardness thing is totally overblown. It may introduce a little more wiggle room for errors, but so does reactive resin. I don't know, just seems like much ado about nothing.
I've bowled in plastic ball tournaments where bowlers sand their plastic balls with 320 grit sandpaper. Gives them a urethane type of look on the lower volume condition.