I think that WotC's "blind spot" is that Favored Enemy was originally flavored as the ranger hating the type of creature so much that he got combat bonuses against it. From that perspective, of course, it makes no narrative sense for the ranger to "switch hatreds" regularly and without justification.
However, flavor it as the ranger recalling combat techniques for use against specific types of creatures, and it becomes less limiting. Something along the following lines, for example:
Favored Enemy
Ranger Attack 1
You refresh your memory of the special combat techniques you have learned to battle specific foes.
Daily * Martial
Minor Action
Personal
Effect: Pick one type of creature, such as Humaniod, Beast, or Aberration. Until your next extended rest, you gain a +2 power bonus to weapon damage rolls against creatures of that type.