Well I didn't even think about using a standard bike carrier
I actually already own one of these and think its great:
What do you think about welding on a 2" receiver hitch and attaching the above carrier?
Having bikes on it would obviously make your signature much wider. You would just have to keep this in mind and remember NOT to lane split
Beauty of it though is that it folds up vertical when not in use (or it can be taken off)
EDIT: Having a hitch would also seem to require the bike to have some sort of mounting location low to the ground. Something the newest Nighthawks and a lot of other non touring type bikes don't have