We were lucky enough to find a 36T chainwheel, with cranks exactly the same length as his current ones, in the magic drawers of the Bike Station. In fact, so lucky, that we didn't realise we'd found them. Our co-conspirator (who unlike me actually understands things like cranks and chain sets) bought it for another refitting job he's doing, thinking it was a 32, but realized later that it was just the right size.
we he disassembled the Islabike, attached the new chainset and off we went. A definite improvement - noticeable, but not so much that it affected his ability get started or to climb. And hugely better on the flats. He still rides it a bit like a bmx, but there's a lot less spinning and coasting.
Which makes me wonder if Islabikes and Frog might want to consider marketing some 'longer distance' bikes, or at least an option of buying your bike with a 32, 36, or 40 chainset? Or even just having these parts available to order?
If our lad found the bike undergeared within 6 months of fitting on it, and riding distances of between 10 and 20 miles, then surely there must be other folk out there in the market for such adaptations?