Actually, I think that escape method was used. At Colditz they even made an airplane and (I think) escaped in that, or perhaps the war ended before they could. To my mind, anything Hollywood proposes as an escape method pales in comparison to what was actually done.

In 1963 I saw a British film based on the the Great Escape premise that totally flattened "The Great Escape" (which I saw later). Can't remember what it was, tho....