Writing, actually scrawling, in my journal has helped me with this. I either have one part write letters to the other and vice versa, or write out conversations between the two.

Having crayons or markers on hand might help, for instance I might find myself grabbing the red crayon and drawing out a big "I hate you!" and more.

Occasionally in therapy I've used the two chair technique, I move from one to the other and speak for that part.

((((((((((((((Rapunzel))))))))))))))

Sarah