I saw a youtube video once where a guy cut a hole in the top of a compact fridge. Appraently the cooling lines were enclosed in the top. Don't take my bad memory as fact, check out the video. (sanyo conversion or something like that)
What I remember him doing was making a solution of baking soad and water, turning on the fridge, "painting" the solution on top the fridge and the heat from the cooling coils (sounds backwards) dried the pasty solution and formed a map of the cooling line.
Another thing you can try to avoid hitting the coils is to drill a tiny hole, smallest you can find into the skin of the fridge, just break through the skin. Then take a sewing pin or something very small and probe around inside the hole you drilled to feel for a cooling line. Many people have done that, me included and it works. You just have to be careful, gentle.
