You could probably build a platform with legs or supports on each side to span your current desk. No need to attach anything to the wall, a bonus if you are renting.
A crude platform could be built out of 2x4's with a layer of plywood on top.
If you want something more attractive, you could use 3/4" birch plywood, with 1x4's glued and nailed to the front and back edges. Sand, stain, and poly and it'll look like a piece of furniture.
Of course, you may want to consider replacing those large, heavy CRT's with flatscreen LCD's. Then you could put up just about any shelf to hold them.