Unless the person is able to tell you to the contrary, assume that anyone with a back injury also has a neck injury.
Place a board, such as a door or table leaf, next to the person. The board should extend below the buttocks (ideally to the feet) and above the head. Keeping the head aligned with the rest of the body, gently logroll the person toward you. Move the board under the person and ease him or her onto it. If the person is vomiting, lay him or her on one side and continue to support the head.
Tie tightly enough so the person cannot move, but not so tightly that you cut off circulation or inhibit breathing. Place towels, sweaters, or pillows snugly around the person, especially alongside the head and neck. Once immobilized, the person can be carefully moved to safety.