I'd done it in Fallout 3 using lenses modeled into the scope mesh, but the refraction shaders weren't capable enough to get a good looking picture through the scope. I just got NV, so I'll see if the shaders have been updated to look any better. (I'll be pleasantly surprised if it is, but expecting the worst...) Of course, you can cheat and do like it usually is (ACOG in MW2, for example) where a different FOV changes the zoom of the entire screen--only without going into a "scope" hud overlay. So yes, quite possible.