Custom page size for the WinDDK Bitmap Driver

I have a print driver based on the Bitmap Driver from the WinDDK. I have
tried to change as few things as possible in the .gpd file, but I need a
custom page size (27" x 16") and I can't seem to get it to work. From
browsing this site, I see that the CUSTOMSIZE page has to fall within the
parameters specified by the .gpd file, but I can't figure out what I'm
missing. Can anyone help me out? Sample code would be great, if there is

Burl Rice
Monterey, TN