Yeh...foudn this way, sorta just came to me heaps of other people probably have figured it out too, but i didnt so i thought id share. Playing as UP had Martha send a full army to invade dutch guana, i only had 3 colonial infantry units there, so what i did was give the region to the barbary states whome i am at war with but martha is not. Instantly martha army is ed off to india, and my army stays, easy just retake the city, they surrender. No units lost
I have also done this in india when i had about 4 armies attacking my one, so i gave the territory to france and it removed all enemy armies and then instantly took it back off france.
Has anyone else done this/got any other ways ?