I have this pull up bar at home and I don't attach it to a door way, you don't need to use any screws either. You just have to twist it extremely tight until its real snug. The customer image on amazon is a great example on how you install it without a door frame.
I use something similar : http://www.amazon.com/JFit-Deluxe-Doorway-Pull-Up-Bar/dp/B001CZ4ZN0/ref=sr_1_1?s=sporting-goods&ie=UTF8&qid=1420568595&sr=1-1&keywords=pressure+pull+up+bar
very easy to set up