The bow is the result of thermal convection within the case - warmer air rises to the top. If one were to "tickle" the starter for a few seconds, some xx minutes after shutdown, it would stir up the air and randomize the rotor positions, thus causing the bowing to be somewhat reversed.
You wouldn't even have to move much air. All that would be required is that all the shafts are kept turning, even very slowly, to allow heat dissipation to be uniform around the shafts. That way there'd be no bowing at all.
You often see engines windmilling whilst the aircraft is on the stand. That's probably not quite going to achieve the desired result; the auxiliaries must stop the one of the shafts turning, leaving it to soak in the heat.