See if you can access a lab supply catalog. There is a device used to cut holes in rubber stoppers used to connect various pieces of glass ware. I don't know max diameter available. The device is basically T shaped - the horizontal being a handle (like a wine bottle opener). The vertical being a cylindrical cutting tool (circumference of bottom edge sharpened)...the diameter determining the size of the hole you create in the rubber stopper. Haven't worked in a lab in some years...might be old tech now replaced by something more convenient. Typically, these came as a "nested set" of multiple sized tools...smaller diameter inside larger inside large etc etc. The rubber we cut was very hard (and thick, 1" or so). Seems like it should work on sorbothane - I just don't know what diameter you are looking for.
