Was just reading this old thread as I am setting up a little workspace.
At my mother's I have two bench grinders on stands in a huge garage my father built. But my own garage is less than half the size.
I have built a custom workbench out of a twin sized oak platform bed (no pics, use your imagination).
My idea was to put holes in the top of the work surface, near the front of the workbench, and just drop pins through the base of the grinder to "fasten" it when it is in use. When not, move it to the back of the bench for storage.
Not ideal, but it solves my space issue. Is this not secure enough? The bench itself is very solid and has no problems handling weight (i have the top bolted down with 10 1/4" bolts).
Similar to a lot of other ideas in this thread, one guy i saw on YouTube mounted a hitch receiver under his workbench and put a number of different things on plates that slide into the receiver when he wants to use them, but i thought that was a lot of weight to put outboard of the furniture...