Bottom line
The Schwalbe Moe Joes setup and seal really well using the ghetto tubeless method. Here's what I did:
Step 1 - tape the rim
As an added precaution when running ghetto tubeless I use a couple of layers of electrical tape on the rim to protect the tube. You could use a rim strip but if the rim strip does not locate itself perfectly on the rim it could cause problems later.
Step 2 - BMX tube
I used a 20 x 1-1/8-1-3/8" QTubes presta valve tube. It was $4.45 from Cambriabike and importantly has a removable valve core which makes adding sealant once the tyre is seated so much easier.
Remove the valve core and put the tube on the rim. It will be a bit of stretch because its a 20" tube on a 24" rim, but you want it to stretch.
Step 3 - cut the tube
You want to cut the tube down the centre line so that it can then fold over the rim beads. A pair of scissors works well for this:
Fold the tube over the rim beads so it ends up looking like this:
At this point, I normally give the tube a good wash with soapy water to get rid of any grease, wax or talcum powder in the tube. You can leave the tube wet and a little soapy as this will make it easier to fit the tyre.
Step 4 - mount the tyre
Mount the tyre on the rim taking care to put it over the top the cut tube and leave the sides of the cut tube hanging out either side of the rim.
Step 5 - air the tyre up
A compressor really helps at this stage. With the valve core removed, air the type up with a compressor. No valve core means the compressor can really put the air in and the end result should be a quick and efficient seating of the tyre on the bead.
Once seated, take the air attachment off, cover the hole with your thumb and bleed the air out slowly. Once deflated the tyre should still be seated on the rim. Take care not to pop it off the bead anywhere and use a syringe to put in a scoop of sealant.
Put the valve core back in and air the tyre up. Give it a good shake around to distribute the sealant.
Step 6 - trim the excess tube
This bit can be a bit fiddly, it all depends on how neat a finished job you want. With a bit of practice you can get a really nice looking finished result.
Grab the excess tube and pull in gently out to put the rubber under tension. Use a razor or sharp knife to cut the rubber along the edge. If you cut it just right it will pull back flush with the top of the rim/bead on the tyre.
If you take a close look at the picture below you'll see how neat it ends up if you do it properly.
Update - 10 November 2010
I also converted the front to tubeless using the ghetto tubeless method. This time around I used a Schwalbe 16"-18" which was the only thing the local bike store had in a "sort of" suitable size with a presta valve with removable valve core. I got it to work in the end but it was a supreme pain-in-the-arse. Basically, it turned a 10 minute job into a 30 minute job. These tubes are very narrow, so with the added stretch once you cut the tube in half there is very little material to hang over the edge of the rim when you mount the tyre. With so little material to play with it needed multiple attempts to get the tyre seated and the tube in place over the edge of the rim.