Screw driver shank, hone a chisel or something similarly hard. Lapping a hard natural a bit can help too.

I was never happy with the scratches left behind by the DMT though. I know it's supposed to just be 'negative space' and not effect how they hone, but it bugs me all the same. So I typically wind up chasing the DMT with sand paper up to 1 or 2K depending on the stone, and I use my Naniwa red brick to refresh the honing surface when it gets clogged with swarf. No scratches, I'm a much happier camper.