I've never treated flint ridge, but plan on going to get some at the end of August. From what I've read take it up to 500-650 depending on thickness in a electric turkey roaster filled with sand raising the temp slowly over time. Mine only goes to 500, but I think I can get it a little higher if I use it in a small space like a closet. Hold this temp for at least 2-4 hours then slowly decrease the temp over time. Once you've worked the temp back to 0, leave it overnight to finish cooling. If you notice no improvement, try it again doubling the hold time and check it again.
I got this info off the Puget Sound Knappers page, so don't hold me accountable if it doesn't work, but this is the method I plan to use.