With the ECU CONNECTED. Basically, you are using that wire to the battery neg as a ground to trick the computer into thinking that it's the clutch switch. Turn on the ignition just like you normally would, touch the wire to the places mentioned instead of pulling in the clutch and then hit the starter button and see if she cranks.
Also, my schematic is showing that Black/Red wire should be going to the side-stand switch. Mine shows the clutch switch should be Black/Orange. What color is the wire at the handle bar/switch side? Try the wire next to that on the ECU.
Since you've already got the ECU plug outer jacket exposed, plug everything back up, apply that battery neg wire to the black/orange wire and see if it'll start.