This instructable shows what a small sharp knife and a 5-gallon bucket can do to help get things running again...oh yeah, you'll also need a bag of quick-setting concrete!
Step 1: The fun begins!
A small slice through the flap of tire I just cut lets a piece of string through to tie the flap back out of the way. The string is white, so it doesn't show very well against the white rim, but if you try to imagine it's there it kinda makes sense.
I also found that this is a tubeless tire, so the next step is missing/uneeded. But if I had to, I would cut the tube in half to pull it out.
Another important thing here is the use of a block to keep the wheel-barrow angled so that the hole I just cut is at the highest point on the tire.
Step 2: The concrete part!
I didn't bother measuring because I intended to get rid of this bag, but I would guess that I used 3/4th's of what there was. More than I thought I would.
I dumped the bag of concrete into the bucket and mixed by hand adding water until I could form a nice 'clumpy chunk' like in the second pic. (that's a technical term...; )