Add JPEG compression filter

I'd love a quick way to apply JPEG "noise" while editing. Often, when compositing an element into a digital photo, I'll attempt to match the grain and compression artefacts by adding noise to the new element, saving the flattened image as a JPG, and hoping for the best. If there was a way to apply that kind of compression and noise to a layer using the filter gallery—to mimic the effects of cell phones and other digital cameras and preview the results in real time—that would be ideal!