Xorg external LCD connected to laptop is not recognized

I am using RHEL6 on a Lenovo T410.  The internal LCD is defaulting to 1024x768, but after I log in switches to 1280x800, which is correct.

My problem is I have an external LCD that is also connected to it.  It's an HP LE2201w that wants 1680x1050.  System-config identifies it as "Unknown" and will not allow beyond 1024x768.

Since it's a laptop that isn't always connected to the external LCD, I'm not sure if a manual xorg.conf is the way to go.

Any thoughts on how to fix this?

lspci: 00:02.0 VGA compatible controller: Intel Corporation Core Processor Integrated Graphics Controller (rev 02) (prog-if 00 [VGA controller])