Well, most of the time you can 1) start up the English/British in any date before the revolution in which they hold land in America, 2) input the cores via the cheat, 3) release the USA as a vassal and 4) then release the vassal, creating an independent.
The only problem with this approach -- indeed with any approach regarding the USA -- is that the designated culture of the USA is "american" and that culture only replaces "english" in 1764, representing the growth of national identity before the revolution. You can't release a country when the provinces and the designated culture don't match. Perhaps you could fix this by changing USA's culture from "american" to "english" in the file usa - united states, but i haven't tested it.
Sort of a rough approach, but it is what springs to mind.