ETpilot, that is pretty much how I do it. Since most of my junk is scratch builds of my own design I kind of have to figure it out as I go. I tend to build grossly overpowered planes, so they end up nose heavy. As I build I place the movable parts on the air frame to see where they need to be. On most of my stuff the entire radio ends up as far in the tail as it will go. If you do this a few times as you go, moving the battery around will usually get you at your cg without any ballast.
Scott.