This is not possible with the currently available notification options and configuration of Notification Centre. The three options you have are
- No notifications
- Banners that stay until clicked
You have no control over the content of the message, its just shows what is sent by the notifying application.
So looking at iMessages, there is no way to change or limit the notifications that are sent by default to the Notification Centre.
So the only solution I can come up with is to turn off iMessage notifications completely in Notification Centre
Then using iMessage's built in ability to run Applescripts when events are triggered, then send your own notifications without the offending content (more private IMHO for work machines) to Notification Centre by using third party scripts.
Of course, those notifications would have your own defined content and would also have to come from an application that is enabled in Notification Centre.
This thread might give you a start on how to create a notification that can be called from Applescript.