Excellent! I had thought about just trying to write something to the file but didn't want to modify the file. It didn't occur to me to write *nothing* to the file :)
I was worried that even this solution might have unintended side effects, e.g., changing the modified time on the file or (less likely in my mind) writing a null character to the file. I tried it on my WinXP system and it doesn't appear to modify the file in any way -- modified date remains unchanged.
"If God had meant for us to think for ourselves he would have given us brains. Oh, wait..."