To go over bluetooth, you could use a third party app (I found one on the google app store called BlueBox that might work). Set the same folder for sync for both Bittorrent Sync and the third party app. First sync with Bittorrent Sync and then with the third party app to the third computer. There's probably a better way to do this with some sort of Ad-hoc network configuration that would allow you to have a shared folder via bluetooth between your pc and android though. That way you don't have to use a third party application.