Hi Bob. Welcome to ETO
I have run across this issue a few times before, and only recently have I found the answer. Unfortunately, it requires two 555 timers instead of one, but you could use the 556 dual timer IC, if you wanted. Anyway, here is the circuit I think you're looking for:
**broken link removed**
Basically, for as long as the switch is pressed, the output will only be on for the set amount of time. If you keep the button held down, it will not re-trigger the output of the second timer until after the switch is released and pressed again. It takes up a bit more space, but it should work fine.
I hope this helps!
Regards,
Der Strom