Ok, here is an idea... get a piece of thick steel that is long enough and wide enough to completely cover three of those bolt holes.
Make a template out of paper, for the bolt holes. Trace that onto your piece of steel.
For the two outside bolt holes, drill them the right size that when you put bolts through those holes into the crank, they center perfectly and tighten it down.
Now before mounting it... Drill a tiny pilot hole in the plate, in the center of that middle hole.
Now, when you bolt your plate to the crank, you have a pilot hole, which should keep your drill on center.
Start with a small drill bit, and work your way up to somewhere near the size of the body of the bolt. Just small enough that you don't get into the threads in the crank.
What is left should be very easy to get out.