I use the word "invented" lightly because I know there are engine stands with something similar built into them already on the market and also I am sure I am not the first to modify mine the way I did.  I used an old hand wench, some scrap steel left over from other projects, as well as some chain, a freehub and a sprocket cassette from a bicycle, to build an easy crank rotation setup for my engine stand.

This is the receiver I built to go in the end of the engine stand.  I cut apart a freehub and welded part of it to the top of the receiver 


The largest sprocket from the cassette is easily mounted to the welded on freehub


These are the pieces I machined to lock the the receiver to the handle holes in the engine stand




This is 1/4" thick angle iron boxed in with gussets and drilled to mount the hand wench.




This is what it looks like fully assembled.




With all the gears the ratio is 10.56:1  It cranks really easily most of the way around, it does get a little harder as it comes back up to the top, but it is still way easier than spinning it over by hand.

Here is a video of it in use
https://youtu.be/2dniOzpRUfU