If you do that you're likely to get it in crooked and mangle the threads, which are pretty soft. What I do is get a long screw with the same threads from the hardware store, thread it in fully, use the cap as a guide, and hammer the screw to drive the star nut into the steerer tube. Make sure you don't drive it in too far, or the bolt won't thread fully into it. When you go to cut the steerer tube, you first drive the star nut in further past to cut point.