I've also hear old print rats talk about adding glycerine to final wash and pegging back to back. Tried in college days and decided it made little difference to the normal-ish DW FB (MCC118 actually) I was using. No idea waht long term effect if any the glycerine might have.

Archival print blotter stacks supposedly work quite well!

Short of the breaking the print's back over a drawer/ruler/etc technique I don't think I've come across a truly successful method that doesn't involve heat somewhere along the line!

Tried stacks of books again, as a student, and gave up on it as folklore after a week or so...

If only RC papers looked as nice. They're a sight easier to handle! ^_^