Should the level of consiousness allow you, i would package the patient prone on the spine board, barring there is no indication that you need to immobolise c-spine (The kidneys are far from the c-spine, and you would be albe to follow the wound tract, as it is not a bullet wound). If this is the case, it is probibly better prone than lateral, as the spine, close to where the injury is, will still be immobolised, and should be better than lateral.
Yes, i have had a few cases where patients have fallen onto pallisade fencing (A fence constructed from vetically placed angle iron with sharpened edges) and had injuries on the posteririor aspect, and the only way we could get them transported was by packiging them prone...