Hi Mark,
That should be possible. Either the forever loop with something like:
FiltCur = 0.99 * FiltCur + 0.01 * ADC*ADC;
DispCur = sqrt(FiltCur);
Depending on what you have in the forever loop it may be fast enough.
Or you might use the 90us Callback to do the sampling.
However you should realize that supply current is not the same as motor power. In fact when braking there may be high current where power is actually negative.