Voltage fault injection possible on switch output?
You might be able to use a Logic Pulser.  It is designed to override the logic state at the probed point with a brief pulse of the opposite polarity of the sensed voltage.  The pulse is so short that it does not damage the device that is driving the signal.  You connect the pulser to the same power supply as the chip that is driving the signal and then put the metal point on the signal that you want to toggle.

Logic pulsers are kind of old school, so many require a minumum of 5V (from TTL days) to run.  The specifications for the one pictured below say that it runs from 3V-15V.  Assuming you are not trying to pulse something with lower impedance than the probe, it should be able to toggle your signal for testing.