There's no real way of doing this with
gnome-open itself, as it is impossible to pass geometry options to the program that will open your designated file.
The only feasible way to specify window geometry would be to set it beforehand in various profiles for your favourite programs by using
devilspie, so that when you run
devilspie will load your profile for say
evince, and set the window geometry as the window appears. If you are using compiz, see this question for how to specify window settings, as
devilspie might not work with all window managers.
Devilspie can be installed from the repositories, and I discuss it in much more detail in this other question. In brief, the configuration file for the target program must be in
~/.devilspie and end in
.ds. Below is an example of one tailored for
; gedit geometry
(if (is (window_class) "Gedit") (geometry "662x742+0+27"))
You will need to specify your own desired geometry that is appropriate for your screen, and put
devilspie in startup applications. You can run
killall devilspie and then
devilspie & so that any configuration changes to files in
~/devilspie are re-read.