Unity Sprite Editor : Include blank/empty cells when slicing?

I have a bunch of *png spritesheets, each divided into 32 cells. On some of the cells, certain frames are empty. When I slice either by Grid-Cell-Size or Grid-Cell-Count, these empty cells are not included. Is there any way to include the empty cells when auto-slicing? I can manually slice, but it is a bit more cumbersome and involves renaming quite a few of the grids.