I would use Photoshop…select each element in your still (one at a time) and copy/paste each back into the composition, then delete the original background. Find a new background and put this below all your elements in the layers palette. Save as .psd, import into Premiere as Layers. In a separate sequence animate each element to “Rain” up, render with no fields, import the nearly finished product into your main sequence and reverse the clip so it rains down.