You get the most interesting things! Guide words would not be useful for this index. My advice is to leave them off. It does break a rule - but the rule is in place for AN INDEX - not multiple forms of an index. I considered suggesting a funning footer that consists of the MAIN entries... but again, those aren't in any order so it wouldn't be useful. Guide words are intended to help someone find information in the index and there is no way to make that happen here.