There is a setting in the SYNC application in Desktop Manager to sync automatically anytime your BB is detected as connected to the PC.
Mind you, that if your BB is already connected to the USB sitting there, and you make a change in your Outlookm you will still need to start the sync. It won't just sync automatically anytime you make a change, but just when you first connect.
I do not know of a RIM/BB solution to your problem, but I use Google Calendar and Google sync to keep calendar info in sync on several devices.
My setup goes like this: 2 way sync every 15 minutes with primary laptop and Google Calendar. 2 way sync between the BB and Google Calendar. One way, Google to PC every 60 minutes, to my office desktop, home PC and wife's PC.
Works very well. Occasionally I will get a couple duplicated entries but nothing worth worrying about or trying to fix.