Multiple Locations in Google Now
I have found that if I search for an address (or other location), not too long after that I get a card with driving directions to that location. If I tap the card, I'm asked if I "care about travel time to this location". Usually I say no, but if I say yes I'll have a new card that gives me the travel time to that location, just like for work or home.

In case you're wondering, the place to edit your work or home is Settings | My stuff | Places.... only home and work are available for me, but maybe they'll add some more custom locations in the future.