you can't do the following because the custom page size won't exist on the system

ps2ps -sPAPERSIZE=A4 input.ps output.ps

This will work (this is 100x200 converted to points)

ps2ps -dDEVICEWIDTHPOINTS=283.46 -dDEVICEHEIGHTPOINTS=567 test.ps output.ps

Never mind this doesn't seem to effect the resultant output... afaict