You might want to run a non-exit node at your home. That way you have a lot of Tor traffic all the time, and the one time you really do need anonymity, it doesn't show up as anything unusual.
I don't quite know how this works, so forgive me if this is a stupid question, but couldn't someone just take the difference between your inbound and outbound tor traffic to find how much traffic originates from your computer?
If the in/out rate of your bridge was both constant And lower than the max in/out rate of your connection, but it seems a bit of a stretch.
(And of course they wouldn't know that it was your traffic to whatever site they're surveilling, they'd just have evidence that was not inconsistent with you actively using Tor to do Something Or Other at that time.)