well this is the only way i could see you doing it unless you have the skimmer level with the tank.... if you got a pump, and instead of using it to bring water in, use it to bring water out, and then use a siphone to bring the water fomr the tank down. however, the only problem is, it owuld have to be EXACTLY the same amount of water going up that is comeing down. And that is impossible to calculate judging the exact amount of air that is brought down, youw ouldnt be able to do it. And then judge the head hieght. And then youw ould have to get an airstone skimmer because the needle wheels and the venturies use the pump. Or you could use a becket is upose. but that doesnt matter, because you arent goign to be able to get the pump and the water exactly right. otherwise, it owuld overflow. and what would you do with a poweroutage? you would have a wet floor.
but if you are lookign to put a skimmer enderneigh the cabinet..... why not jsut get a sump?!!!!