Sending a sysex message of [0x00,0x20,0x29,0x03,0x03,0x12,0x00,0x02,0x00,0x01,0x01] from GP to the SL61 MKII will put the controller in ‘Automap’ mode, and make the controller think GP is automap aware - you can then control the lights / encoder rings via sysex msgs.
You could then map the widget to the encoder on the SL61 and add script to send the widget value via sysex whenever the widget value changes.