I have seen in catalogs a set of black plastic cone-like risers to
do just that. Sorry I can't tell you where.
I've seen such at Bed-Bath-& Beyond, online and Mall Stores.
Probably also at similar household specialty outlets? Cones and
blocks, white and Black (+?).
On the other hand, my first thought to this inquiry, was to think of
making a table sized, 6" - 8" tall riser, open only on the back, to
give a convenient, out of sight / mind, storage place, for POP
supplies and over stock, handy and out of sight, and rapidly packed
up after a show, ready for next time.