You could try this:
Set the knife on its spine on the WE base, and use the angle cube to find the WE base angle. If not zero, use the zero offset. Then, put cube on side of blade so that the cube will not interfere with the knife going back onto its spine. While supporting the knife while on the WE base–it will be quite top heavy– read the angle.
Use the cube after the blade goes into the vise to try to match the same angle. This means the spine will be parallel with the base (laterally) and the spine-to-edge line will be perpendicular, therefor straight up and down with respect to the vise. Fore/aft tilt is up to you.
I could have done it 5 times while writing this. It’s not hard, but it might feel like you need three hands at first.
You could also use a rotating or pivoting protractor.
Hope this helps.
