I'm currently talking to my architectural blacksmith pal to build me an auxiliary rack out of stainless tubing to make it easier to carry soft panniers. It's pretty simple, but I don't have the skills to build it. It'd just hook on the lower rail and bolt into the spot that holds the mushroom for the Vario upper mount. Not quite what you're talking about, I know, but I'd think it would be easy to adapt something like that to 3rd-party hard cases as well. Now that the 2013 models come with the Vario rack as standard, I'd expect to see someone start making these for sale. (Mine will be a one-off).