A broken arm? Sure. But, a leg? What are you thinking...
My first thought that comes to mind is YOU CAN BE SUED.
Unless the patient signs that they WANTED to walk and that you adamently offered to wait for a rescue vehicle due to their stable condition, you are totally liable.
Our major concerns with fractures are ensuring the patency of distal perfusion, and stopping a simple fracture from becoming a compound fracture. Both of which are achieved via splinting, and limiting mobility. Walking, completely defies the entire purpose of our care.
What I WOULD have done, is called for a stokes or the quad you spoke of with the rescue sled as well as an ALS unit capable of pain management. The pain management because quads aren't exactly built for comfort, and due to the extended removal time.
NEVER would i walk a lower extremity fracture. NEVER EVER.
If he started to walk on his own, I would sooner let him go and document it as him fleeing the scene on his own merit than me allowing him to do so.