The challenge is to minimise European colonial expansion after Leopold acquires the Congo Free State. I'm already thinking of having Britain undergo a revolution 1870-ish, so that should blunt one of the main actors. And Prussia will have been defeated in a Seven Weeks War with Austria and France, so no Germany yet. Would France slow down without Britain as a strategic rival in Africa? How many native states and non-European powers can survive in Africa by this point?
EDIT: I don't mean PODs must be after the Congo Free State, only that that should be one of the final acts of major European colonial expansion in Africa.