I wish I would have caught this thread earlier and saved you some time. I was going to suggest using a different key or even a long, thin nail file but I see you figured it out. The indicators are purely mechanical and are simple push button resets that any long, thin object can access and reset. They are not even dependent on using a designated key for the car - master or otherwise.
As your manual states, don't ever reset them while the car is moving. You can damage the fragile plastic gears if you force a reset while they are turning. This goes for the trip odometer, also. I learned the hard way. When I reset the odo while in motion (84 Accord - same gen but MMC), there was a *crunch* and I could never reset it back to 000. It only reset to 002 after that.
I was going to suggest using a different key or even a long, thin nail file but I see you figured it out. The indicators are purely 
