As noted above, the 5A starts at L'Enfant Plaza. If you're determined to do this (and I don't think it's an unworkable plan--maybe I just have unreasonably good luck, but every 5A I've ever ridden has had luggage racks), board there, not at Rosslyn--especially if you were going to have to Lyft across to the river to get to Rosslyn to begin with.