I once saw 240V going through a barrel plug. Still gives me the willies just thinking about all of the ways that could go horribly wrong.
The IEC connectors are pretty well designed.
My advice would be, since it seems you have the space for the IEC connector but the time drilling the hole is the bottleneck, to look at buying a punch for them. They're pricey ($100+) but worth it if you have to do a lot of connectors. You could also make yourself a jig to semi-automate the procedure yourself, if you can get a little mechanical advantage. My experience doing just a few at a time, drilling the biggest hole you can and then attacking the corners with a dremel (cut wheel) and/or a nibbler does the job just fine, though, you're right, it is a bit tedious.