Eric,
It's not that hard to get a tap started straight, just get a piece of material as thick as the threads on the tap are long, drill it so the tap just fits through it. Clamp it to the flange in line with the hole, you have your guide that way. Easy and straight. Of course the best way is just use the mill to do it, no problem if you have access to a mill. I just through it up on my HMC and push the button.
Curtis