Use a Bi-Metal holesaw, such as of Lenox or Starrett origin. I don't remember the size I used, but it worked great and all I ended up with inside the bar ends was a thin metal ring. Then bumped the ring remnant, it turned 90 degrees then pulled it out with some pliers. Use high sulfur cutting oil with the holesaw and you will get better mileage with it. A holesaw arbor, a pilot drill bit and the holesaw will cost you more than just taking Ian s advice and buy some similar after market bars of the same configuration. I already own all the tooling, so that's how I did it. If you do decide to cut the plug out, remember a 3/4" holesaw cuts a strong 13/16ths hole+ in metal, so your holesaw size required should be 3/32nds to 5/32nds" smaller that the I.D. of your bars, at a minimum.
