Using a biocube as a sump?

[freezetyle]

So i have been looking for ways to add a sump to my biocube without drilling it. which is seeming to be quite troublesome as i do not want to use a syphon overflow. so my plan was to use the cube as a sump.

Just looking for a bit of input. I have put this idea in my tank journal but figured i would get more responses here.
my idea was to place the tanks side by side on a stand similar to this one

This was i can have basically a display tank and a display fuge/frag tank/ jawfish house. I have having some problems working out the plumbing. I would put the return pump in the first or second chamber and have the return running through the third chamber or possibly straight into the display tank through the nozzle that is already there(if there was enough pressure. my main concern is obviously the limited amount of space for reserve water in the b/c. but it may not be a big problem as the new DT would be roughly the same size with the addition of an external overflow.

Suggestions?

[freezetyle]

anyone?

I guess the main concern I am having is to use the stock pump that is in the third chamber or like previously posted just to bypass it to keep chambers 2/3 empty to allow the overflow of water