ok. is it possible to run the water out pipe directly into the tank?
if you can, just take the air pipe, without the stone, and keep it near, under the outlet of the filter. Hope that makes sense.. that should work a charm.
discus don't mind airstones, or bubbles... but they don't really like change, lol.. so this is new for them and may freak them out a bit, but they will be fine.