Try using some threaded rod or some stove bolt of about the right length. Capture the chisel between two fender washers and hold those between two nuts (maybe wing nuts would be easier). Adjust the position of the nuts so that the chisel is whatever angle you need. In use, the chisel would ride on the sharpening stone while the bolt end would ride on the workbench. If you want a microbevel, slip a couple of business cards under the end of the bolt and hone the micro bevel.
I use this technique routinely. Before I start sharpening, I color the bevel of the chisel or plane blade with a permanent marker - this allows me to quickly see where the stone is taking off metal and I can adjust (shimming under the stone or bolt end) for a perfect sharpening. Consider this contraption to be a guide which helps hold the blade at the right angle - the sharpening pressure goes on the blade.
Bruce