There is a ledge to the right of where the pains rock is. You have to jump off of that and onto his rock. To get to the ledge, go forward to where you continue on with the game, but instead of going through the tunnel, right at the entrance there is a rock ledge that goes around the right side of the cave where you fight the pain, go along it, and it will take you to the cliff, then just jump off it and onto the rock where the pain usually is and pic up the box. You now have the camo.
Voted Best Nazi Mod Ever <3