Add a comfortable passenger backrest to your 30 Liter K-Max Topcase (Sku: 0400-1067) for a very reasonalbe price.  The installation is as easy as 1, 2, pie as the only two tools needed are drill and a screw driver.  We recommend using old timey drills to make the job a little more entertaining.
While you're at it, why not consider adding the LED lighting kit for the 30L K-Max Topcase (Sku:0400-1071)