I recently bought a Kona Unit, primarily for winter commuting. After getting it home, I realized that though there were mounting points on the front fork for fenders, they were conspicuously absent on the rear.

After experimenting for a bit and making little progress, I went back to my LBS for some help. They came up with a solid and aesthetic solution. (Mad props to Phil at Full Cycle!!!)
I've attached some pictures in case anyone else is in the same boat trying to figure out a way to fix a similar problem.

I'm not sure where they got the clamps from, as the closest I was able to find online after the fact were "earthing pipe clamps" (for grounding) or "three bolt pipe clamps". Neither seem to be as thick as the ones my LBS used, though I suppose round clamp might have some advantages. The rubber liner they added should prevent any slipping or rubbing.

Not only were they able to create an attachment point for the rear stays, but through a clever use of spare parts and some dremel work on the rear clip, they kept the lines clean and maximized the amount of clearance to allow me to run larger tires. (2.1" studded should fit with the sliding dropout all the way forward.) By moving the mounting point, it also solved the common issue of clearing the disc brake caliper, without the need for any spacers.

They also made an "extension" for the front fender mount, to compensate for the fork adjusted 29er front end. This allows the fender to sit lower than it would with the stock hardware.

The last thing I need to do is put on my studded tires, then sit patiently and wait for snow!