Most people have a power drill (cordless or otherwise) at home. You can get the Ryobi 2 1/2" hole saw and it will make short work to cut a hole in any wood, plastic or firm rubber that you want to cut a hole for your Anova.
(ignore that their picture is of the 2 1/4" hole saw - it IS the 2 1/2" one you want):
Ryobi's page for the bit:
Once you have the hole, check for fit - if you have a little bit of room left, you can edge it with electrical tape to provide a really good seal for the PC. (and, having a hole, as opposed to a U-shape, you don't need to use your clamp - the PC can sit in the hole).