wouldn't you just have to load all renderpass images into multiple layers and not position them by hand? don't have photoshop myself but found this:
in CS4, Bridge gives you all the tools you need to import images into multiple layers in one Photoshop document.
1. Open Bridge.
2. Navigate to the directory that your images reside in
3. Select the files. You can click and drag around them, or use the shift button to select multiple files.
4. Now in the menu bar select Tools > Photoshop > Load Files into Photoshop layers
and i am sure there is gotta be a import as new layer
thingy somewhere, not?