Replacing a rear innertube

What Dicki said :)

Of course you could tie up a spare tube under the brake bridge to the saddle ready to go, then roll the tyre off and switch them over with the wheel in situ.

But really HTFU :D

Fixedwheelnut almost had it. In fact, you'd need to have the spare inner tube looped inside the rear end of the bike. It would end up looping around the non-drive side chainstay and seatstay, effectively running parallel to the seat tube. You could zip tie half a dozen there if you're a really unlucky person. You'd need a sharp knife to a) cut out the old tube each time you punctured; b) cut the zip tie holding the new one. Then you'd just pull it around to the inside of the rear end and put into the wheel. This is such a shit hot idea, I may even write in to Viz!