It matters if you want the ball to be legal without going past the legal weighthole specifications. Don't tell him to put the C.G. anywhere, I'm sure he doesn't want it swung left and have to have a weighthole on the negative side of the ball, what would be the real sense in that unless you wanted to try a 135 degree drilling.
To answer your question, any driller should be able to determine where the "Actual C.G." is with a dodo scale. Lane 1's website has a nice tutorial on how to find it.
--------------------
-DP3
Respect the Game