Ok, I'm pretty happy about this. I got an Antec NSK-4380 case, and while it is pretty good, it needs a couple small changes.
For one, on the power supply compartment on the mobo side of the case, there should be a hole to route unused power cables out of the way. So I cut a hole about the same size and location as the hole on the other side.
Another hole was needed in the front of the case, down low near the base, so that the mobo jumper wires for power, reset, HDD light, etc, could be routed down inside the faceplate compartment and not clutter up the interior of the compartment with extra wires. So that required another, small round hole.
Now I couldn't fold the metal, and I didn't want to risk cutting the wires on the edges of the sheet metal (still a little sharp, even after filing), so I went looking for a suitable material for protecting the edges. I wasn't having much luck, and figured I'd have to go with electrical tape, when I stumbled over the answer:
In my basement I have some stuff for repairing window screens. One of the items is this thin, round, rubbery, vinyl "spline". It is pretty thin, but it has a hole through it, and after cutting off a section, it was pretty easy to use a sharp pair of scissors to cut a line down the length of it, so that it could be opened.
It's flexible, but a little stiff, and not super easy to get on, but once on, it really holds nicely and effectively prevents cutting from the metal! In the square hole, by the power supply, I used a little super-glue to make sure it stays, but the round hole has enough pressure all the way around it that it doesn't even need the glue. Another plus is that it is about the same gray color as the case frame, so it doesn't stand out, visually.
I hope this helps some folks out!
If ye love wealth better than liberty, the tranquility of servitude better than the animating contest for freedom, go home from us in peace. We seek not your counsel nor your arms. Crouch down and lick the hand that feeds you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen. - Samuel Adams