I liked the idea published by Etienne Labuschagne in his thing http://www.thingiverse.com/thing:776611
I printed couple of clamps in ABS and played with the joint.
I noticed couple of issues with his clamps design:

1. The joint is quite weak on forces in pull apart direction, though it works well when you push clamps toward to each other;
2. The clamps are too spatial. Being using in my delta machine base it would lose significant amount of build volume in X/Y plane.

So I decided to make my own design to avoid the issues mentioned above.

The carriage designed for bronze bushings (8mm (d) x 12mm (D) x 15mm (L)) for 60mm distance between linear rods. It has adjustable GT2 belt tensioner. The carriage together with clamps give 24mm offset in printer radius (original Rostock's carriage gives 22mm). Note that the end-stop screws holders are at non-standard positions (for my custom design).

The platform together with clamps have 33mm offset in X/Y plane, the same as Rostock's platform. It has the same mounting holes and thickness, so I just was able to use hot-end holder and z-probe designed for Rostock platform use in this setup.

The mechanics in action - https://www.youtube.com/watch?v=lkXnUtAfmqY
It is still under testing and investigation. For the time being it's worked for ~ 22 hours in printing mode and all parameters are ok so far.

[2015-07-13 updated with some instructions]

[2016-03-03]
The joints still work fine. But my machine has other issues, so I decided to redesign some parts...
Investigating OnShape's features tried to reproduce the clamp. It came out better than old, more stiff and strong, so that I decided to put it here. Check new_clamp.stl and its source https://cad.onshape.com/documents/56d8a036e4b004367d917f94/w/7628c58a47d2143045023c61/e/6a2a69d3abcd3062a0b15a0a