True, an auger type bit is useless on sheet metal, but will work on maleable plastic like ABS. I have used an Arbor press with dies for things like 15 pin D shell holes and Centronics type holes, the press , a manual mechanical 1 ton , will cost only about 60 dollars, but the Centronics sized die was well over 100 dollars. I have no idea where you could get a 1/4" square die.
For fairly thin plastic, and small quantities you can resort to drilling central holes, the scoring the square shape and snapping off the remaining bits. This will also work in a pinch for light aluminum, provided it is a fairly stiff alloy like 5052, that has been hardened. Unfortunately most face plates for small project boxes likely use 3003 or 1000 series, which tends to deform easily and not snap at the score line.
One other idea is to take the time to make a really nice square hole in a piece of scrap steel, then use it as a file guide on the plastic holes. Drill pilot holes in the plastic, clamp the guide plate to it, then use a small file to finish the hole, the guide keeping you from removing too much material.