I use a 55 gal
and have a Marineland 350 bio-wheel on the right side of my tank. It works more than efficiently for my setup as I use an underground filter as well.
While the PVC
idea is nice, it might end up looking tacky aswell. What I would suggest is getting two smaller ones. I know marineland sells smaller ones of the caliber that I have, with one bio-wheel and the 2 slotted back to back filters, instead of the dual slotted back to back filters. So that way you can put one on each side.
Depending one your tank, you might not need to extend that though, is your tank overly dirty? What size tank do you have? What kind of filter system are you using? Do you have it directly uncovered by a window?