Non-square pixels LCD

Of course, this is not a FreeBSD specific question, but maybe somebody used to solve similar issue.

How to deal with a non-square pixels LCD, for example Newhaven 7"?
The graphics is distorted significantly: the DPI difference (X vs Y) is 7%.
Setting the DisplaySize option in xorg.conf doesn't help (should it?).

Thanks for ideas!
It works for me with the Nvidia driver.
From /usr/local/share/doc/NVIDIA_GLX-1.0/README, disable EDID-computed DPI by setting this option to false :
Option "UseEdidDpi" "False"