Play-tested Cow’s idea (of putting all of South America under US control, thus increasing America’s starting production by 8, and giving 11 additional infantry at the start of the game) and it seemed to work reasonably well.
It also seems like a more organic solution than simply tacking on some arbitrary number to USA’s income, and has some historical precedent (since South America did lend some support to the war effort)
Coupled with a modest bid for the brits (6ish), i think this would go a long way to balancing the game.