'Hide empty staves within systems' on only SOME parts in MS4

I have a score where the percussion parts consist of more than one instrument so I want to make instruments hidden when they are empty / not being played. 'Hide empty staves within systems' under Format > Style > Score achieves this, but it hides empty staves in the piano parts that I have in the score too...I want both staffs to always be visible for the pianos. Is it possible to 'hide empty staves within systems' for only SOME parts?

Thanks!

EDIT: After close inspection of the MS4 handbook, I see that there is a way this is supposed to work, but that does not seem to work for me...Is there any sort of workaround that anyone's aware of?