An update on my last post having finally managed to speak to a very helpful chap in the DGAC in Paris.
What he told me is that it is illegal without an AOC to offer air transport services (ie an aircraft and pilot as one service). However, it is legal for third parties to hire an aeroplane without a pilot, and then hire a pilot separately to fly the plane (as long as he is qualifed to fly the plane).
The above is quite correct and is the de facto situation with more or less the entire light jet scene around the world (most of which is not owner flown but the owner hires a professional pilot/crew).