P: Find keyword by synonym

When searching for a keyword in the keyword list (using the keyword filter) only matches with keywords but not those matching with synonyms are displayed.
In Lr 2 also matches of those keywords were displayed which had a synonym match.
I would like this to be an option in Lr 3, too, maybe user-definable.
Usecases: I've got a large list of keywords with most of them having at least one synonym (my keywords are in German and I use synonyms for english translations and other synonyms). (1) When I look for the existence of a keyword I would like to make sure that I've not included it as a synonym already. (2) While searching for a specific topic sometimes I can only remember the synonym (yes, growing older...). In Lr2 I could find it easily by keyword filter.