I still think this is a good possibility. As for the head having limited movement, it may work to their advantage that the dragon's neck is still in shackles at that point, as you can see in the released image.
Also, if all of the surrounding scenery is screen based, then they could theoretically make it appear that a stationary dragon head is moving by moving the whole environment around it. Add to that the motion of the RV, and I think it would be nearly impossible to tell that the head wasn't moving.