Buy two Vice-grip type pipe chain wrenches. (The ones with what looks like a bike chain to wrap and lock around a pipe.)
Take the bike chain off of one and added it to the other.
Now you have a pipe chain wrench that will wrap around the harmonic balancer and allow you to turn, or lock the crank as needed.
I made one years ago and it comes in handy every time I do a timing belt or adjust the valves.
You could also to the electric starter bump. But I always miss my mark and end up turning the crank by hand any way.