Can I mount a doorway chin-up bar in the hallway rather than in the doorjam?

I recently bought a pull up bar made to be mounted in a doorway however i would rather put it in the hallway so that i can mount it up higher. The doorway is not tall enough to be able to do a pull up without bending my legs... I would like to be able to start from a hanging position. Any advice?
8 answers 8