OK, I've built bumblebee and it doesn't work. The problem, interestingly, is EXACTLY the same problem I had in the logs when I was just trying to run the drivers in a headless mode: no screen!
I've tried every value I can think of for "ConnectedMonitor" and yet I still get the unhelpful message:
Invalid ConnectedMonitor request; request for for '', but the
valid display devices are ''.
No display devices found for this X screen.
Screen(s) found, but none have a usable configuration.