Hmmm I was going to ask you what size drill bit. Lol. I think a drill would give you the cleanest holes without cracking or splitting. I drill holes in plastic flower pots and things all the time. I have a bit that I would try first but haha, I don't know what size it is, I'll check and see if it's labeled when I don't have acat sharing my blanket on the couch. Maybe someone else will have an answer who has done this. Have you looked on craigslist or anything for cheap booda domes? Some people have luck finding stuff they want, I don't.