I got the micrometer out and measured the bushing and the hole.
The bushing is tapered and this measurement is up the top at its widest.
The hole has a little body filler and finish etc hanging around the top of the hole.....so close but not too much.
My view...maybe others have done it correctly....get some dowel...thick enough to give you a dimension of 10mm.
I think most people that have done the hole filling have had to find a dowel that had the fluted sides and sand it down smooth.
So you need a dowel that gives you a smooth side of ten mm diameter.
I would suggest gluing the holes and re drilling to the size you thinnest end of the bushing measures.....so just under 10mm.
I wish you luck....I don't think epoxy on its own will hold the bushing in against the pull of the big bass strings.
**I just had a read and thought about my advice. I don't think 10mm will help.....I think the hole you will drill needs to be 10mm...so the dowel will need to be thicker than that I think. Oh, I hope somebody else with better skills can help.***
You will then have the issue of the earth wire hole.....ouch.