That did the job, thanks! I grabbed the bb image of a BNC connector from core parts, rescaled it a bit to match the space (the barrel isn’t long enough but close enough!) removed its connectors and pasted it in to bb giving this:
which with your background makes this about as good as it gets I think. This is the latest version of this part with the above change in it.
PH_meter_1.fzpz (65.6 KB)
In this case the “board” is made up of 4 line paths (in a rectangle) and 4 arcs (the curved corner pieces), I expect @KingDarBoja did something similar to what you suggested to get them in to a single path that described the area so it could be filled. In any case, the final result looks pretty good .