This is very easy to do if you own the "man the guns" dlc. Simply follow the British focus tree for "revisit colonial policy" as this will release your overseas territories into independent nations that have the option of either joining your faction or distancing themselves. There are about 30 nations or so that end up getting released so its ok if some dont join. Alternatively you can also follow the tree to become communist by going down the "a change in course" and "concessions to the trade unions" focuses as this will force you to choose "revisit colonial policy" and completely decolonize to avoid a civil war. This time if they dont join you will have war justification and can just puppet them.