I'm a sharpener by trade, using single bevel heads, and I freehand sharpen the tantos on a flat hone(not a machine you want to pay for, but you could do the same on a stone, if you can hold the angle. I'll have to try your suggestion, Ron. I do use your KME in hunting camp, and it is a real good tool.
It's a little hard to visualize the centerline of the head on a 25 degree single bevel, but if you get the tanto right, the arrow will still spin perfectly to confirm broadhead alignment.