Perhaps moving the "bathroom" area is not the solution, but making the bathroom area sanitary is the way to go.
I put a piece of wax paper (roughly 4"x4"
on the spot my gecko goes to poop. The wax paper keeps the turd isolated and prevents any liquids from getting soaked up into the substrate (which also prevents bacteria growth and other nasties things from happening).
Also a note on bacteria growth and sand. Sand is extremely absorptive. If your gecko pooped on the sand, then chances are alot of the urea and other waste products from the poo got absorbed into the sand in a much bigger area than you might think (think of how a drop of water spreads on a paper towel). This then gets kicked around by your gecko and gets spread to the far reaches of his tank. This is one of the reasons most VETS say not to use sand (or any particulate bedding), and rightfully so since it becomes a bacteria breeding ground if you don't change out the sand very often.
But if you use the wax paper trick, this problem should be reduced somewhat.
-Lemur 6