Dave I would just attach a piece to the fence that would support that piece at the right height and then clamp a straightedge to the table for the other side so that the work piece stays firmly against the fence. If you click on my Uploads button (down below my user name) you'll see the home made fence I am using. The faces come off quickly and slide together or apart to keep the opening close to the size of the bit. With this design you could have one set of faces for routing this piece and still be able to quickly and easily replace them with standard faces for regular routing.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.