You could do something like this:
Make yourself a tileset. With a modular tileset like this, you could make just about any shaped terrain you wanted easily by snapping the pieces to the layout grid and rotating them as needed. Use the tileset for your collisions. Changing them around for level testing would be fairly simple.
Then when your design is in place, and your level plays how you want, grab some screenshots and stick them in the mesh editor as a template. Then tweak your meshes so they fit over your tiles, save the meshes, and place them in your levels over the tileset pieces.
Edit: ARGH, newt beat me to it