You could hang an Oxy/Acetylene torch on your plasma cutter for thicker stuff. You would need two batches of code (outlines on the plasma & holes with the torch), but my torch cuts straight clean holes down to 3/8" id. I have to play with some scrap to find the kerf size on every new tip size/thickness I try. But by trial & error I can get it to cut uniform holes every time. As the holes get smaller, pre-heat before pierce becomes a narrower window. Too short and I don't go through, too long and the puddle ends up bigger than the hole. I make notes on pre-heat time, feed rate, tip height, etc. for each tip/thickness combo. As I do more, I have more notes and less trial & error. It is too bad plate isn't more uniform as far as metallurgy, just when I think I have a size nailed, I'll get some plate that reacts differently to being cut. Some plate just plain sucks.
Heck, once you try the torch on thicker stuff, you may use the plasma less. My $150 hand torch kit claims 5" max. Not that I care, I doubt I'll be cutting much 5" at home, but it teaches 1/2" a lesson. MIKE
PS, my torch button pusher involved about $50 in parts. Depending on your machine it may not be too hard to retro fit a hand torch onto it. I've seen alot of pics of commercial machines with plasma/Oxy torches on them.