I have just discovered that there is still a vestigial part of the old way of being in the Beeminder code. (I hesitate to describe it here lest you take it away from me, but perhaps it helps me in the meanwhile).
Even though the full goal borders don’t turn blue when a goal is due, I have realised that the dot that is currently positioned showing the current status of the goal moving up (or down) the graph actually DOES show the colour (blue or orange) that takes into account weekends off etc etc as described above.
A wonderful early morning discovery. 