hey dude,
my W Widows are no more than 18inches tall and to keep them short and bushy i just tied the main stem down at an angle. Its so easy to do and doesnt stress the plant like topping. These pics are after about 23 days 12/12 and as u can see they are looking fine. Oh its called LST (low stress tying) and if u search these message boards for 'lst' ur bound to find something of use but it aint brain surgery.
hope this helps