I don't know, Matt -- aside from cosmetics and weight reduction, I'm not sure that they make any difference in the rocket's flight, so if the simulated rocket doesn't show them, it's probably no big deal. As long as you account for the reduced mass by correcting it with a mass override, that is. But with all of that being said, I believe that there is a way to do it. I'm not sure, but I think that you draw or create the sections of the fin that are all around the holes. In other words, you plot the solid areas (the fin material that is there), and don't plot anything in the voids (the holes).