My simpleton thought on this is that the airlines will use our donations to lower their book liability on outstanding miles.

As I understand it, some(if not all) airlines have on their books the liability of FF Miles outstanding. If this is true then us consumers and holders of those miles help lower that liability. So keeping track of the donated miles and passing those along to those needing the miles would be important, at least from a GAAP standpoint.

Of course I could be wrong on everything above.