In reply to MonkeyPuzzle:
in a nutshell:
A 2 litre fizzy pop bottle, with top.
Two old valves, with securing rings, cut out from tube, but leaving some rubber attached (enough to make a seal), or two old tubeless valves.
Remove the core from one valve.
Drill two holes in the bottle top, allowing enough room so that top itself will still seat and seal properly on the bottle, and far enough apart that you can get a tube and a pump onto them. Different length valves may help but mine works fine with average length valves. The holes are about 5-6 mm diameter - I can't remember which. Fit the two valves into the top and screw them firmly into place with the rings; a bit of silicone sealant may help to get a good seal. Screw your fuel pipe or similar onto the valve without the core. Screw the other end of the tube onto the tyre to be inflated, fold the tube in half and hold it folded with a hair toggle.
Fit your pump to the other valve and pump the bottle up to about 100psi. If the tube blows off, it just goes 'fssssst'. No sign of a bottle popping, but 100psi seems to be enough, and it's not going to go bang, just fsssst.
When you're ready to go, pull the two halves of the tube apart so that the toggle pops off and all the air scoots into the tyre. If you can hear air escaping between the bead and the rim, push the tyre there to help it seat. Once it's on, I tend to pump some more air in with the bottle still attached to make sure it's properly seated - nothing worse than having it pop off again just when you think it's sorted. Well actually there is, the wheel then falls over and sealant goes all over the floor and you get a lecture about doing bike things in the kitchen....