Well Colin,
I slice my driver and fade my hybrids (3,4,5) when I setup SQUARE. A square setup works just fine for my other
clubs.
So, when I'm on the course, I'll close my stance (put my trailing foot further away from the target line), widen my stance a bit, and think 'flatter swing'. It results in a swing that would otherwise be outside the target line, but results in a straight shot.
Unfortunately, I have no long range practice facility close by (to work on a full-time solution), so I only have a temporary fix to offer.