You can use imirie shims as upper entrances. Supposedly, using this hardware will not encourage bees to build comb within this additional space. Brushy Mountain carries this item. I bought three, but haven't employed them yet.
You can also use this shim on the uppermost super when storing supers off of hives to guard against wax moths. The shim creates a dead space to place your plate of moth balls on top of the frames while allowing a plywood cover on top, without crushing the moth balls.