In Valve’s 9 November status update, they mentioned that little SDK business, as well as providing information and some pictures.

Here's a sneak peek at the plush Weighted Companion Cube coming soon to the Valve Store. Your rear-view mirror will want a pair of companions, too.

I’m disappointed they’re not actually cubes, but Lorithad says he’ll be buying one. I still prefer the more puzzling solution to this problem.