I just installed bumblebee on a Dell XPS L502X. It basically works: optirun glxspheres does exactly what it should. However, X is running with a resolution of 640x480. I can try to change settings with optirun nvidia-settings -c :8 (as suggested on the bumblebee wiki), but in the relevant section it only lists resolutions up to 640x480. In the /etc/bumblebee/xorg.conf.* files, there are no Monitor or Screen sections. Adding them doesn't change anything. How can I change the resolution?