Centering the display

[Grant]

My TV doesn't seem to include its native resolution of 1366x768 in
it's EDID data.  Hmmm.  Anyway, it does include 1360x768 and runs fine
like that.  This does leave a strip of 6 pixels on the left side of
the screen.  Can I center the picture so that there are 3 pixels on
either side instead?

I think I can do this with nvidia-settings, but I don't want to use
that package just for this unless I have to.

- Grant