You can't do it using setSize in the same way you can't do it with window.resizeTo.
Alternatives are OS specific:
Linux:
Need to enable virtual screen resolutions, e.g.
xrandr --output LVDS1 --mode 1366x768 --fb 2000x3000 --panning 2000x3000
Where 1366x768 is the real display resolution of your physical display. And 2000x3000 is the virtual resolution you want to achieve.
Windows:
Need to enable Remote Desktop Connections on windows machine.
And need to connect by setting up a custom resolution, for example from linux command line:
export MACHINE_IP=10.0.2.15
export WIN_USER_NAME=brendan
export WIN_USER_PWD=secret
rdesktop ${MACHINE_IP} -u ${WIN_USER_NAME} -p ${WIN_USER_PWD} -x b -a 16bpp -g "2000x3000" -r sound:off
Mac:
idk if exists. feel free to edit and add one