Every once in a while my girlfriend and I will take her Wii remotes over to my Dad’s house for some Wii bowling, and having to synch the remotes every time was getting really annoying. I couldn’t find any information about using your Wii remote at a friend’s house in the manual, but after digging through the Nintendo support pages I finally found how to use your Wii remote with a friend’s Wii without synching it. It’s called One Time Mode Synchronization.
One tip: in my limited experience you need to add the remotes after you’ve loaded the game (instead of doing it in the Wii menu) or you’ll have to do the process twice. Definitely nice not to need to resynch your Wii remote when you get home, though.