God, I feel like such a moron posting about this here, but I'm seriously miffed.
I've seen bodies thrown over railings, such as the side of the Maria Narcissa, in Splinter Cell Chaos Theory. However, I can't seem to do this myself. I stand upright next to the railing facing outwards, and hit spacebar. The body is placed at my feet on my side of the railing. It's a totally stupid question, but what the hell am I doing wrong?
If you grab someone and walk up to a railing you can throw them over the railing as a kill. If they're already dead/knocked out, the best luck I've had is carrying them to the railing and then turning Sam so the body is close as possible to the edge. Then hit shift, and if you're lucky the body'll make it over the railing.
There's no foolproof way to find it that I've discovered.