Truly bizarre. (I think one can assume that the support added to 275.19 was not just detecting that it did not support the GT 540M!) Was there anything strange in the /var/log/nvidia-installer.log that was created during Bumblebee installation?
I can only suggest posting all relevant logs with as much verbosity under a new thread with a catchy title like
/var/log/messages: "The NVIDIA GPU ... 0df4 [GeForce GT 540M] ... is not supported by the 275.19 NVIDIA Linux graphics driver release"
to attract some expert opinion...