You should check the openfts(tsearch2) mailing list
http://sourceforge.net/mailarchive/forum.php?forum=openfts-general I believe this was discussed there before.Also look at tserch2 version in PostgreSQL 8.2. It allows creating something like synonyms for this type of thing.
http://www.sai.msu.su/~megera/wiki/Thesaurus_dictionary
