By the 1980s Stronglight actually made an interesting tool for their sealed cartridge bearing BB set which had a threaded shell. It held to the face of the fixed cup using the axle and crank bolt. Looks like a pretty well conceived design and I suspect it would have worked with any similar fixed cups such as the "Competition" cups of the 1970s - which had two opposed flats (like a TA or Campy N/R). Here is an early 1980s Stronglight catalogue page with the ref. 720 tool seen at the bottom:
Unfortunately, even if this tool was found somewhere, the earlier octagonal BB cups had very different dimensions.
The VAR # 30 tool was offered with a few different jaw blocks available for use on fixed cups from various manufacturers. That would be a very handy (albeit expensive) tool to own. Perhaps worth the cost for ultimately protecting the flats of all those old BB cups which we always seem to struggle with. Certainly wish I had one. Best alternative I've found is a bench mounted vise with strong precise jaws for firmly holding the often shallow flats of a BB cup... then rotating the bike frame off of the component.
BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA