Do you have the line diagram of the sump. I'm contemplating something like this on the sides. One side for the sump and other side for a DIY CO2. Use 4" on both the sides on a 36" tank.
If you look in post #11 you can see a pretty good shot of what I ended up with but I do not have any diagrams of what I did.... I like to work in my head when it is something not involving school or work. I feel I can be more creative this way.
I have thought about running an immersed setup with wrap around it and a CO2 airline going in as well. It will just keep pumping and work itself out as pressure builds. Seems feasible to me.
I thought of this as well but i haven't gotten around to refilling my co2 tank so it hasn't happened.