Get your monitor's
EDID and save it to a file. You can do that from Linux, with read-edid.
Then go to Windows and get the parameters for the working mode. I no longer remember the details (I had to do this only once, and it was a few years ago), but there are Windows utilities for that, and they're pretty easy to find.
Then edit the
EDID file to include the new mode. I think I wrote a Perl script at the time, but you might be able to find other (Windows) utilities to do that for you.
If you end up having to do the plumbing yourself, the format is described at Wikipedia, and there are a few posts here that might help you, such as this, this, and this. In particular there's an edid-generator program that looks like an useful start.
Beware that the order of entries in the
EDID file is important. If I recall correctly you want your preferred mode first.
When you have the cooked
EDID file copy it to Linux, and point
xorg to it. Back when I did that I had to add an option like this to the
Device section in my
Option "CustomEDID" "DFP-1:/etc/X11/EDID.bin"
xorg.conf, so you'll have to hunt around to re-enable it. The
CustomEDID is documented in nVidia driver's docs; you'll need to adjust that too, to fit your particular setup.