I don't use LR to print and I don't know about LR4, but I have LR 3.6 on this computer and there's a "Cell Size" set of sliders in the Print module that will downscale your photo to whatever size you need. I would suggest first creating a Virtual copy of the image in your Library, then use the Develop module to crop it to the proper aspect ration for the charm (looks square but I don't know), and then print from the virtual copy.