Ah! There’s the problem. The easiest thing to do is to get a piece of 2x4 or any small piece of wood. Heat some of the shellac up to get it into a ball in a small fireproof container. I’ve found this is easiest with a torch since things like heat guns cause the light flakes to blow around too much. Once you have a little blob of it (perhaps around a nickel-sized piece), you can place it on the wood, melt it into place and then put your piece on it. You just need to be careful if you use a torch as it’s easy to burn the shellac. It won’t really stick then and you’ll need to scrape the burned layer off.
Once it’s on the wood, it will stay put and you won’t have to go through that initial process again except to maybe add a bit more shellac from time to time. Otherwise, you just heat it up until it runs, set your piece on it, wait for it to cool and off you go! To get the pieces back off, I find it easiest to stick them in the freezer and then pop them off. Any extra or residue can be cleaned off by letting it soak in denatured alcohol.
Hope that helps!