Here's the thing: I rather suspect
@Faeelin's got it right. The Galloway Plan isn't going to be accepted by Britain, on account of the fact thst it's too late to come to such a solution. It could be done earlier, though. I don't think the Albany Plan back in '54 had any real chance, either, mostly because Britain was wary of giving the colonies more power, and because the colonies feared a central government with tax-raising powers. So that one was... well, too early.
But in 1764, Prime Minister George Grenville in OTL first proposed direct taxes on the colonies to raise revenue (needed to repay the war debt). But crucially to our scenario, he
explicitly delayed passing the act, and apparently on the grounds that he wished to see if the colonies would propose some way to raise the revenue themselves instead. While probably not super-enthousiastic about such a notion, he likely knew that imposing direct taxation would cause all sorts of trouble. Letting the colonists cough of the money themselves was just plain easier. The colonists didn't come up with some brilliant solution, and the next year, Parliament passed the Stamp Act. We know what came of
that: even though it was repealed a year later, the Declaratory Act that followed did insist that Parliament retained full power to make laws for the colonies "in all cases whatsoever". The Sons of Liberty had been founded already, grievences had come to the surface, and the whole issue became a ticking time bomb.
So, a POD: Benjamin Franklin, who was very annoyed when his Albany Plan was rejected by the colonial legislatures (accusing them of being "narrowly provincial in outlook, mutually jealous, and suspicious of any central taxing authority"), learns of Grenville's attitude and (presumed) motivation early on. He sees his chance. Assembling a gathering of colonial representatives, he puts the case before them. They may dislike a central taxing authority, but the alternative will surely be the British Parliament taxing them all directly. "It it must be done, best that we do it ourselves."
Franklin's proposal - which is, in fact, much like the Albany Plan and the Galloway Plan - is sent to Grenville, who correctly identifies it as an opportunity to prevent a lot of trouble later on. The Stamp Act is indefinitely postponed, and some negotiations on the exact furure of British North America follow. This becomes a whole congress, dealing with all sorts of tangentially related matters (such as the exact westward borders of the existing colonies, and the westward limit of expansion). In the end, a compromise is reached that both Parliament and the colonists find more or less acceptable. The North American colonies are placed under one or more central government(s), in which they enjoy representation, and which may tax them. Via this tax revenue, Britain is repayed for the costs of war. Because of the extensive negotiations, Americans are more at liberty to move west than they were in OTL. The Townshend Acts, the Tea Act, the Quebec Act and the Intolerable Acts are all avoided.
All of this depends on both sides being sensible and keeping a cool head, which is not a given-- but I do think there was a brief window to get the ball rolling there, and in OTL, the Americans let that window pass them by (apparently because they weren't even aware of it). A man like Franklin being slightly better informed at just the right time could make all the difference in the world.