1. Use paperclips to connect sparkplugs to sparkplug wires so tip of plug isn't covered by boot.
2. Start bike, and let warm up.
3. Put it up securely on centerstand.
4. Put in 3rd gear
5. At idle short out just one cylinder with screwdriver and observe mph on speedometer while running on one cylinder
6. Do the same on opposite cylinder.
7. Adjust idle screws so each cylinder runs at the same indicated mph. Adjust low cylinder up, high cylinder down, or split difference as needed to maintain desired idle rpm.
Off idle balance is checked the same way with the throttle held open in some manner that wont allow it to move.
Success depends on the individual. I watched Sergei at IMWA do it this way and get it spot on as confirmed after with twinmax, I can get it darn close, some don't have the ear and feel for it. Some can do it by ear without the speedo.
IMO, its a workable solution in a pinch, but I prefer the ease, speed, convenience, and accuracy of using a good sync tool.