I have completed a MOD that allows for multiple categories. You can see it here in the Crafts category: http://www.indexuhelp.com/aWork/brow...fts-344-1.html ( at least until I change the site )

The Film@ category belongs to the Photography category and the Rodeo@ category belongs to the Sports category

Just to show you that you can include ANY category, I included the Saddles@ category from the Sports category and the Bookmarks@ category from Publications > Books > Accessories.

The cost of Multiple related categories is $15. Installation is also available for $15.