What do you mean balance?
You can change the component center of gravity in the xml file. Look for the <component count="number"> block in the xml file and you can change the values for the "centerOfMass" for each component. The numbers are XYZ values.
You can place a transform group in GE and set the numbers in there is get a visual of where the "centerOfMass" should be then copy those XYZ Translate numbers to the xml file. You do not need to save the transform group you make in GE.
Hope that helps.