Yes, I have found this method to be a viable option. However, I think I'm going to be more proactive and carry a magnesium rod:

Apparently, those magnesium rods from are softer and easier to scrape than those big Magnesium bars from Coghlan's and others. By using separate magnesium rods, I can save my more expensive ferro rod to light 1,000+ fires. cool
If you're reading this, it's too late.