You're not supposed to be able to, but sometimes it happens. I booked 2 rentals (1 with "free days" and 1 with "1-2-Free" free days), with my name on one and my wife's name on the other in LAS. I pulled up to the gate with her in the car behind me and mentioned it to the gate agent and they said, "Odd, they're not supposed to let you do that, but whatever" and let us both out. I wouldn't count on it though.