/etc/bumblebee/xorg.conf.nvidia

Section "ServerLayout"
    Identifier  "Layout0"
    Option      "AutoAddDevices" "true"
    Option      "AutoAddGPU" "false"
EndSection

Section "Device"
    Identifier  "DiscreteNvidia"
    Driver      "nvidia"
    VendorName  "NVIDIA Corporation"
    Option "ProbeAllGpus" "false"
    Option "NoLogo" "true"
    Option "AllowEmptyInitialConfiguration"
EndSection

Section "Screen"
    Identifier "Screen0"
    Device "DiscreteNVidia"
EndSection