My DH broke his collarbone 10 years ago in a cycling accident. He did not ride at all while it was healing, which I think was a good choice. As others have said, you do use your upper body when cycling, and it's just not good to stress a healing bone in that way. And you wouldn't want to risk a fall -- it's just not worth it. The bike will still be there once you heal, and eventually this forced time off will only be a distant memory. I can personally vouch for that as I was laid up with a fractured pelvis three years ago myself.
Heal well...take this time to do something else. Variety is good anyway!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow