You can incorporate your core muscles into your back workout using exercise and bosu balls. A great exercise is to stand on a bosu ball (to use your core muscles) then you use a cable machine that you can adjust so that the cable hook is just below chest level. Next, attach a row bar. Using the row bar stand arms length away from the bar then grab the bar and pull it in directly below your chest, extend your arms and repeat.
You can also do rows on an exercise ball provided that you can accurately perform the movement without the ball interfering.
You can buy an exercise ball here starting at $20