I realize you found your solution but another possiblity are old Veco alum spinners, yes I realize the are not going to be commonly avalible but can be had. I have a nice stash of these and here is one I recently installed in this RC airplane.

The stepped back plate is just under a 1/16th and like to save these for the short shaft situation where a true spinner is kind of a must.

As already mentioned the Fox prop shaft extensions are not the solution for this but if any are interested as said the are avalible for either 1/4 or 5/16th shafts and either half inch or three quarter inch extension.

Here is one on my short shaft Fox 59 and they function fine:

John