Instead of jumping into the foxhole, lie down next to it as close as possible on its left side and the game will allow you to qualify in the prone rather than the standing position.
When you are able to modify your M4, go to your Personnel Jacket. Choose the scope you want to use, then select the M203. When it tells you that you cannot use the M203 with the scope, turn off the Xbox. When you turn it back on and go to your Personnel Jacket, you will have your M4 equipped with a scope and a M203. Note: When this glitch is activated, you will not be able to use the iron sights correctly. You can only use the 4x zoom.