I made a video of this here

Steps are:
1. Click one of the switch handles and pause the game without releasing the mouse button
2. Release the mouse button
3. Click and hold the right switch handle, and use the frame advance key a few times as you move your mouse up, not releasing the mouse button.
4. As soon as the red light comes on, keep the emulation paused.
5. With the game still paused, release the mouse button and then click the middle red light, do not release the mouse button.
6. Unpause the emulation, nothing should change, now drag your mouse up.