I just prop up my stones in a rubber stone holder onto my other stones at whatever angle I need (I have to mix and match the stones to the right height for whateven angle I am shooting for) with the backsplash of my counter as a backing so the stones don't slip. The adjustable rubber stone holder holds the particular stone I am using securely and an angle indicator like Blues's picture shows to make sure the stone is at the right angle. I try to hold the knife as close to horizontal as possible, and I get pretty crisp and defined corners where the bevel meets the primary grind, so I am doing something right as far as holding my angle steady. Of course it is still freehand so the edge itself has a tad of convexing in it, and I usually finish with the final grits a couple degrees above the main angle I sharpen at to make sure I get rid of the burr and have a durable edge. A vice like Blues's is really nice and something I want to look into, as it is a pain in the butt sometimes to mix and match my DMT stones and Spyderco stone holders to prop my stone holder on, but it has worked for me for the last couple years and I am pretty happy with the results. My outlook is that the price is right and I am happy with my edges, even if it seems like a half ass setup.
Mike