A friend has a piece of square steel tubing (I think it was 3", about 6 or 8 feet long) with a trailer ball at one end (don't remember how it was mounted, but I'd assume just through the top wall), and a coupler at the other. As I recall, it was pretty thin-walled tube, but he was only launching a largish SIB.
Somebody over here made a tongue extender kit that was essentially what Cod described: The thing slid in under the center trailer frame member, and, when needed, was slid out to some kind of stop device, and pinned in place. Max length depended on what kind of obstructions were behind it on the trailer.
The problem with the first solution is that you need to ride on the jockey wheel, or the whole thing collapses to the ground. The second method has at least some rigidity, and acts like a really long trailer tongue.
Backing with the second method shouldn't be too bad; it will turn slowly and really wide, but for fairly straight runs, should be pretty straightforward (no pun intended, unless it's better than it appears.)
Here's the second setup: