hmmmm i know exactly what your talking about. you could either
1. put another container under the one you have to use as your res and put the water/ sumbersible pump in that so the one your plants are in give your roots maximum space. just get a longer tube to connect the pump to your sprayer manifold... that is what aeroponics is growing in air.
2. if you dont do that then you will need to get an airpump and airstones and put those in the water to keep it aerated or the roots sitting in it will rot.... if you do this you will have yourself an aeroponic/dwc system.