The VSS signal might still be available
Typically, the instantaneous vehicle speed is calculated by the ABS controller using one of the wheel speed signal rings.
At that point, and within the ABS controller, the speed 'value' is placed in a data packet and sent to the instrument cluster on the CANbus. That's how the instrument cluster receives speedometer gauge information. Another example of that is the ECU sending RPM data to the instrument cluster on the CANbus.
In addition to the above, the ZFE controller constructs a VSS signal for use by the GPS. Though Rdcyclist says that possibly the VSS signal is no longer available in the harness. But there is still hope.
Even if there is no longer a VSS wire in the harness, the ZFE controller might continue to create the VSS signal, and still provide that signal to the same pin on the ZFE controller connector.
EDIT: For 2010 and later bikes without the blue/green VSS signal wire. From the schematics, the blue/green wire carrying the VSS signal comes from pin 42 on the ZFE module. So even if the blue/green wire is deleted from the harness on the 2010 and later bikes, the VSS signal might still appear on pin 42 of the ZFE controller.
Poolside screwed with this post 10-25-2012 at 06:48 PM
Reason: Corrections concerning the source of the VSS signal