"Yeah I'd love to try Scotland, be great to do Fort Bill and McMoab, slight problem is that I don't drive. "
Train to fort william, ride to nevis range, sorted. I'm told that the nevis red has similiarities in riding and steepness, and it's the longest sustained tech descent in the UK. Nothing like as high so you'll not get any altitude conditioning though. If you book well in advance, the trains aren't too expensive, it'd probably be a very good set-up for the mega.
Oh, and a load of upper body exercises! Everyone complains of arm pump, UK cyclists generally don't work their upper bodies very hard, slow pressups to failure was how I trained for motorbike racing and the arm pressures are, I think, going to be pretty similiar.