I appreciate all the comments and suggestions.
Yes, Master L is the only one on the back for now and I'd be happy to get some bits (stem & bars) to make it fit with a view to all bits being recycled in some way when it comes to Ms Lardy's turn in a couple of years. I should explain that the bike's a bit small for me (which I'm happy to live with) so my saddle's a bit far back. In fact, I've just bought a slightly longer front stem so that I can take my saddle a couple of cms forward and make space for the stoker. From the comments, I think I've realised that its the rear top tube that's short which, along with the short arms of the young chap, limits the amount he can lean. So I dont think flipping the bars would work. I take your point, fboab, about whether he needs to lean at all - perhaps I'm misleading myself when I see how he sits on his own bike - although he's the one who piped-up and said that he's not comfortable. The cow-horn bits of the bars are bent such that they have three hand positions, something like:
__/
/
and I've tried to imagine any combination of bar angles and stem extension (stoker stem is fully extended, I think) and I just can see it. I shall experiment thios weekend and report back.
Is it just me, or is the stoker's top tube length fairly short? It seems to me that once Master Lardy has grown another few inches and started leaning forward to any degree1, his face is going to be not far at all from the small of the pilot's back.
Seems to me to be the beginnings of a business case for a grown-up tandem in due course...
(It has taken me nearly an hour to write this whilst looking after my 2 year-old - clearly I'm no good at multi-tasking).