In that case synonyms is the best of all choices for sure. However wildcards are not supported there.
I just updated the knowledge base with more documentation about index table related hooks here. Those let you access the keywords, fields etc.. before they are indexed. If you are into custom coding, then using the asp_indexing_keywords could help you out. That is basically the keywords array for each post iteration before they are counted and sent to the database. Maybe you can try programming a custom function to manipulate them, or to add more based on your criteria.