If you guys need to center mount your bindings to pull off anything, you need more practice. The binding is not meant to be drilled there because of the thinner ski and the curve of the edge. You are going to have a harder time setting your edge to turn, the longer tail is harder on your knees in a fall, and you are probably going to have a hard time getting the ski warrantied if something happens.
1 cm forward is one thing, but most twin tips already have a progressive stance. Don't do it.