put it in personal.xls, or create an add-in from it (creating personal.xls is probably easier).

I've never used a personal.xls file, so my details may be sketchy...my understanding is that if you dont already have one in the xlstart folder, you can create one by saving a workbook with the name personal.xls, and storing in the xlstart folder. I'm sure Google can help you find instructions.

I'm not sure if the Mac is different; I suspect that for this, it is not.