Larry,
Obviously what you say would work but would be a major and costly retrofit. The utility, after all, owes you a Neutral. The dream gizmo would install almost as easily as a surge arrestor, keep the voltages to Neutral balanced, not waste power when it isn't needed, and scream bloody murder (or log) when it is needed. Since you would have to load down the lightly loaded leg to achieve balance, the power would be wasted if you had no desired load for it.
Joe
