Pillage them all before capture or do not capture... however the OP said without building, nothing about not capturing. 30 pop cities are roughly the sane limit apart from the odd city that you can pump higher. So 8*30=240*.5=120 science. You would have to rely on a lot of pillaging to make up the shortfall or take all cities so you have say 50 cities to get 500 science. It is possible but as Lily hints you cannot remove campi and so have to frig with natural play to avoid it.... but the simple maths is yes if playing ultra violently. Playing peacefully turning off all other options it would be a long old game.