Codiqa lets you mock up your JQuery Mobile apps without installing any software. My big question here is the pricing. It seems a bit steep considering there are other mockup sites out there that will likely soon add jQuery Mobile to their list of possible mockups. My big question is, why Codiqa over other mockup options? They do give you a nice 30 day trial and you can actually "use" the interface after mocking it up by sliding around all the elements.
Worth a look.