Hat rack with which device to enlarge holes?

Hello people, I bought for only 40€ a few Kenwood KFC-2089ie with 20cm diameter today in the shop, had already boxes in the back, believe 12cm. Of course, they do not fit in the old holes, I noticed that you can not remove the hat rack at all and have laid me over there and started with a drill and a grinding attachment (from the material as well as to the knife grinding) to make the holes bigger, but it took a long time since the metal is very hard, I Don’t like the same procedure. Does someone have an idea of how to make it faster, or a trick? Don’t have soo much tool to choose from, and with a jigsaw you don’t think there’s a round circle in it. I’ll try it with a rounded arrow lg