Any question answered...

Is there any such thing as a screw on disk brake mount that could be screwed onto a fixed fixed hub? or am I just making things up now?

Think your making that up.

It has been mooted in discussions about making a fixed disc hub - take a fixed/free hub and screw an adaptor onto the freewheel thread. I don't think anybody has gone in to commercial production, but it would be a trivial task for any ordinary machine shop to make one. Just a cylinder of metal with a female 1.370x24 thread and 6 equispaced M5 holes on whatever the ISO PCD is. Screwed on brakes are known to work, it's common practice on tandems.

it is been done.... http://urbanvelo.org/montano-velo-fixed-hub-disc-adapter/