For more information, join the team subscribe to the mailing list
at the bottom of the Launchpad page
http://launchpad.net/~hybrid-graphics-linux
Please join this team if you are new by clicking on the "Join
Team" link at the right of the Launchpad page. It's important to
have as many users in the community as possible to request for
appropriate support.
One of the team member found a way to switch on/off the card on the Lenovo T420 4180W1H model using this acpi_call script:
https://lists.launchpad.net/hybrid-graphics-linux/shmIj3d0AfAT.sh
This email has all the details:
https://lists.launchpad.net/hybrid-graphics-linux/msg01387.html