I did find a workaround, you can unscrew the silver part from the mount end of the lens and shim it inside there, mine already had a shim I could use as a template to cut more.
I have no idea where to get a shim the right size, so I cut my own from post-it notes. I think I have 3 in there, it is not quite perfect yet, but I can stop down to f/2.8 and it will be sharp focus at 8mm.
Adding a 4th post-it is too much, then there is a wee bit of extension....I will need to find some different kind of paper to shim it more accurately.
For now I am satisfied.