Instead of glueing an entire scalp on a round ball, which might be difficult, just cut a narrow strip of fabric the will be the "part". Place your yarn perpendicularly across it and sew down the part. Then glue the part to the ball where ever you want it. Then put the yarn/hair back and form into a small bun and put glue on the back of it and pin in place. Bobby pins will stick into the ball.
Just my 2 cents worth