I should mention that for wet-molding to work, you need specific types of leather. Chrome tanned leather which is what you normally get at the stores is likely to be unsuccessful becaues they often put a mild waterproofing agent in the mix and therefore the leather doesn't soak up the wax like it should. So you land up with a really ugly mottled look. If you want to wet-mold, you need vegetable-tanned leathers or any other sort of leather that will soak up the wax. A simple test I do is to stick my finger in some water and draw it across the leather. If the leather soaks up the water and darkens immediately, it is ok for wet-molding. If the leather repels the water, do not buy it for wet-molding. I thought you should know this as the majority of the leathers sold in Aust are Chrome tanned and I don't know what it is like for you in the States.
Basically wet-molding is the process of molding the leather while wet into the shape you want. You can build a mold like Singteck suggests or you can 'cheat' which is what I do. I take the object that I want the leather to fit (in the case of the USAF it is the sharpening stone) and wrap it in clingwrap to protect it from water and anything that can leach out of the leather and use that as the mold. You need to wet the leather thoroughly to make it pliable and soft -- a soaking it in a tub of water is good. Then you mold the leather over the object that you have clingwrapped. You will need to clamp the leather down while it is wet and leave it undisturbed until it is dry so that it will keep it's shape. Once it is dry, hotwax the sheath and you are done. Note that if you do the wet-molding, you absolutely _need_ to hotwax the sheath because if you don't and the sheath gets wet, the whole thing will go out of shape again. The good news is that hotwaxing is easy and inexpensive and you only need to do it right first time to get very durable protection.
Good luck and post pics of your sheath when you are done -- would be great to see your project.
Btw, very nice sheath Maquahuitl -- very rustic!