Split inner tube?

At Moab

  • , a couple of people mentioned that there exist inner tubes which are split–so you can install them without taking the wheel off. This sounds great to a Pashley owner. But I can’t find them anywhere obvious on the net–where can one purchase such a thing? Or do you just cut a normal inner tube and somehow close off the ends?
  • I only mention Moab to make those of you who weren't there jealous again.