Yes, you can! At least as of a few weeks ago At check-in let them know you want to self park and they'll bill your room and activate the room key for the garage. Easiest way to get from the garage to the Waldorf mostly indoors is to enter the Signia and walk to the back of the hotel towards the conference rooms. Then you walk the very long hallway connecting the two hotels. Just an FYI the room key didn't really work for the garage while I was there although they were supposedly working on it. Have a great trip!