Joined: Jan 2009
Posts: 6,645
Likes: 2,373
From: Colorado Springs, CO
Bikes: 2015 Charge Plug, 2007 Dahon Boardwalk, 1997 Specialized Rockhopper, 1984 Nishiki International, 2006 Felt F65, 1989 Dahon Getaway V
I commute with a backpack on a rack. I would get a rack, a cushioned bag for the briefcase, and bungee it to the back rack.