Photoshop: matching images with liquify filter?

Hello, I am trying to fix some proportion problems on a sketch. I have the photograph on the bottom layer, and the drawing on the top. The best way is to use the liquify filter, the only problem, is that when I use the filter it only shows the active layer. So I cannot see in real time if I am moving the shapes to their appropriate position. It's very tedious and counter intuitive to just keep moving little by little and hoping that the images will eventually match up. So how do I go about having the photograph as a template underneath the sketch while I apply the filter?