turning a seaclear wet/dry into sump

Hello all, this is my first post. I have a 75 seaclear system II tank built into a wall so there is no room on the sides of the tank for a skimmer. The opening in the rear where the bio balls and drip tray are is only about 4" wide but is the height of the tank (obviously) and I have about 15" above the tank. I heard of some making teh wet/dry area into a mini sump area. I want to add a skimmer so I can make it into a reef tank or at least manage nitite levels but I can't figure out how to do it. I want to avoid driling holes in the tank and adding a sump below as that will be too much and I will lose valuable cabinet space below, well, my wife will . Any ideas are appreciated.

 

I added photos in the lmajor32 gallery if it helps

 

I just purchased a system 2 and will be drilling a hole for a bulkhead fitting and adding a sump. I thought long and hard on this but don't see any other way how to get enough flow without creating a ton of little bubbles that would return to the tank. I'll be turning the bioball area into a refigium.