When I needed to punch some holes in some shim steel I just made a simple punch. It was also 1/4", so I ground a likely looking profile on the end of a piece of 1/4" HSS bar I had lying around, then drilled/reamed a hole the same size through two block of steel. Put the shim between and tap the bar with a hammer and you get a nice hole. If you need to punch a lot of holes this might be worth it, otherwise, as the previous reply says, just clamp it between two bits of wood and drill through it.