I use the very small bulldog clips, such as this one:
http://thumbs.dreamstime.com/x/bulld...p-10506456.jpg
During my experimenting/playing around, I ground away at the lip at the bottom where the levers attach, which reduced the angle. This still gave an angle that was too high, so I hammered down the top part which looks slight crimped, which served to thin the clip down. The resulting angle is easily below 20 degrees but to be exact, I'll have to measure it later on this evening.
The clips are no longer easy to apply since they have to be crammed open with a screwdriver and then applied to the spine area of the razor. There are also issues if the razor has a hollow spine area that is not straight, since the clips do not follow exactly the curvature; although, they can be bent under heat or just cold, so that they do.
I'm not entirely happy with the solution although it does help a lot for honing true wedges and razors with crazy spine-wear. The clips have the advantage that you can flatten them to adjust the angle that they give you but it does tend to mean you have to repeat the task for individual razors. I'm kind of tied for time on the bench so I haven't been able to try it on any other razors than the true wedge I've been experimenting with - I do hope to be able to continue with them soon. An engineer could likely make an adjustable version of this idea, would be an interesting project.