xorg.conf: setting up scaled desktop ?

[Toerless Eckert]

I've got this old projector that has 1366x768 native resolution,
but will not correctly display VGA/computer signal at native resolution,
and 1280p resolution has stupid overscan.

The way how i solved this under windows with NVidias drivers is
to output 1080p video signal, which the projector will accept, and
then have a desktop resolution of 720p and configure underscan such
that it will be quite accurately displayed 1:1 on the projector.
This trick doesn't work natively with the NVidia drivers, instead
i can only achieve this by display cloning, where VGA is the primary
display set to 720p resolution, and then the video signal is cloned to
the YUV connector set to 1080p  resolution.

So, i was wondering if it is possible to configure something like this
in Xorg. Even if this is also only possible by cloning and appropriately
setting underscan.

Any exampe configs with nvidia drivers for cloning and underscan ?

Thanks
    Toerless