26/12/2014: Modified height a little, and increased the tolerance so that it's not so tight.
Here's a two-part clamp for adding a hot-bed and glass bed set to a Mini Kossel. The bottom part lifts the hotbed above the aluminium frame so that the two thermistor terminals don't short out. That part has a little embedded trench to allow for a couple wires and solder to be added to connect the thermistor without problems. The top part is the sliding clamp which is used to firmly press against the 170 mm glass bed and hold it in place. The design is such that the full surface of the glass plate is available for printing; the glass is held by firm sidewards pressure and downward pressure from the top clamp being pushed down by the screws. It's quite a tight fit, so if people are having problems I will adjust the tolerances a bit. I purchased the hotbed from AliExpress for about $20.
You will need two M3x10 screws for each clamp. I used M3x12 and snipped off a couple mm off the end, worked just fine. Put the screws through both parts first, then screw onto the screws in the 1515 tube but don't tighten. Slide the part over the hotbed edges, with the hotbed going between the two parts. Now start to tighten clamps a bit each, making sure the glass is centered and pushed down, by pushing the sliding part against the edge of the glass and holding firmly while you tighten. When it's all finished, the glass should be held firmly in place against the hotbed.