Use a bandsaw, hand saw, grinding wheel, driveway pavement, whatever and grind a flat spot on the nut at one of the points.
Make a waste block in a 4 jaw chuck, put medium CA on both the nut and block, mate them together, then blast with accelerator.
If you have a screw chuck, you can also make a mini waste block, screw it on, then glue the nut onto that block.
You may be able to get a tennon on them, but they're so small that it would be better to put a tennon on some wood, then glue the nut to the wood. You need to do all you can to keep from wasting any of the nut. Most of them are the size of walnuts with a few jumbos being about the size of small chicken eggs. They're creamy white, most have a void in the middle, they'll also turn caramel color if heated with friction.