From the pictures I have looked at it seems like the RH-PI107 cone would be compatible from a the bearing race surface perspectibe and could work with a spacer as you suggest...the only issue may be if the cone screws in so much that the wrench flats fall within the dust cap making the flats inaccessible...you would have to try it to find out or wait for someone who has done this to chime in.

Here is a source for the cone:
http://www.bikeman.com/HU9855.html

-j