I still say that the best way to handle this (assuming that you have no chance of being promoted over your boss), would be to get him/her one of those "word of the day" calendars where the word that is described is obviously not the right one. This should clue the boss into her/his own vocabulary failures. You should be able to find one at novelty shops.

Also, put it in a box with no return address and leave it with the rest of the mail so that he/she can't trace it back to you....just in case.