O.K., one attempt, one failure. The largest acrylic globe at Home Depot was 8" but since it was less than $10 I got it since I knew I would probably break it anyhow. I didn't want to splurge for the hole saw and got a dremel for Christmas so I thought I would try it. First hole did pretty well. It was a little rough around the edge but nothing the ear globe didn't cover. I probably go over-confident on the second hole and cut too fast because as I got to the end of the circle a piece flaked off that the ear globe would not cover.
Things I learned about using the dremel:
1) go slowly
2) it seemed to cut better going counter-clockwise around the hole.
3) cut the hole smaller than the opening and then use the grinding stone attachment to even it up.
4) have an alcoholic beverage waiting either for celebration or to ease frustration.
Just as an experiment, I was able to take part of the piece I had cut out and make a patch for the area that was flaked off. Glueing it in place from the inside of the globe, I don't think it would have been too noticeable when the light was on.
I decided to save my ear globes to use when I find the right size head globe though. Can I use this?
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053