The skill Profession requires a creature to put at least 1 rank in a Profession skill specialty to use that Profession skill specialty beyond the Profession skill's most basic use. (The Profession skill's entry Untrained says, "Untrained laborers and assistants (that is, characters without any ranks in Profession) earn an average of 1 silver piece per day" (Player's Handbook 80), and that's pretty much all there is about untrained Profession skill checks!)
In official or third-party material, is there a special ability that enables a creature to make untrained Profession skill checks as if the creature were trained in all Profession skill specialties?
This special ability can be granted by a feat with few prerequisites, an inexpensive magic item, a race with no Level Adjustment, a base class, or a prestige class that is relatively easy to enter; the more uncomplicated, the better, and the more consistently available, the better. If no other options present themselves, a spell (preferably low-level therefore suitable for making into potion or putting into wand or eternal wand) could work, but that's a last resort: I'd like the creature to be able to practice any trade without first having to employ a spell effect.
Note: Keep in mind that while an answer could generate a list, such a list should not be unbounded and will likely be quite short. While I suspect it won't be an issue given the request's obscurity, if, when composing an answer, your list appears to be running long, narrow it to the least complicated and most consistently available options (as per the question), but perhaps still mentioning in passing complicated and inconsistently available possibilities. (More can be read on Meta about the site's stance on list questions in this question.)
Anyway. While building sample characters for an upcoming campaign, once again I happened upon one of my favorite feats, the Secrets of the Mantis feat Military Mind (79), Secrets being part of AEG's Oriental Adventures line and bearing the Wizards of the Coast-approved seal. The Military Mind feat's benefit allows the creature to use its Strength modifier instead of any other ability score modifier when making Knowledge, Craft, and Profession skill checks. (Yeah, I know! I was thinking Conan the Librarian, too! High five!) Obviously, leveraging this with feats like the Complete Champion feat Knowledge Devotion (60-1) and the Dragon #339 feat Craft Expertise (34) make the Military Mind feat more fun, but, because I'm struggling to get access to a number of Profession skill specialties to make that part of the feat's benefit worthwhile, I'm wondering if there's a workaround.