If you're rush-capping UK, picking up DEI is trivial. If IJN declares on you over that, it's THEM who are at risk of getting fuel denied (naval bomb them off coast of indonesia, keep your convoy routes from west coast of that island, intercept trade routes from middle east/venezuela outside their air cover).Unless you take the Dutch East Indes, Siam and later Japan do not have enough rubber to sell your whether UK is still in the war or not.
Or just sink their navy and conquer them too.