I am not sure what you mean by mounting it. I guess you could rig it up somehow, it sounds like you are wanting to do a small closed loop. It would be much easier to by a mag pump, say a mag 7, and just run a plain ole closed loop. In general, you would have one piece of pvc in the tank ( or sump, although I haven't seen that done ) running down to a pump, which you could mount behind the tank, and then hardpipe it to the scwd so as to give it something to sit on so you could avoid trying to rig it up. Then just run the returns out of it like you planned on. It would be a very easy install and would probably take longer to get the parts than to get it working. I would go with 2 3-way elbows so you would have actually 4 seperate water flows. Here is a pic in case you aren't sure what I mean. Just get them in 3/4 being that's what the scwd returns are.
I am not sure how big your tank is, but you could even go upto a mag 12 to really push the scwd and eliminate some more powerheads. The scwd is rated to 1400gph now, I hear they are coming out with a 1" model, which will be able to do more.