You might consider trying the "fill pattern" feature to create a bunch of holes. To do it, you can create one hole, then use the fill pattern to select the boundaries you want to fill and adjust the spacing.
The more holes you have, the nastier your performance is going to get, but it's worth a shot.
I agree with Steven, patterning all the perforations will kill your system performance, even though it is a simple feature.
I recommend the following:
1. Only make a small area patterned to show that the part has holes. Use a note on the drawing to tell of the extent of the pattern.
2. Make and pattern the holes with the sheet flattened rather than in the formed part. Holes that intersect/straddle a bend are properly bent and deformed if done this way. If they are made in the fully formed part they might cause the flattening to fail or could be difficult to pattern, but could be even more difficult to model in the first place.