I get that it's traditionally for reviewers to post what they're looking for, but how about a provider using it to post a cattle call for certain clients she's in the mood for?

Post away.......but you may have better luck posting an ad on your regional ad board spelling out your taste of the day. Either way, I like the idea of a cattle call to draw in the right boys to suit your mood.

It is an ISO after all. Just don't make it an ad. (no link to your website, no picture, no contact info etc.)
Worst case scenerio is TER will pull the post if they don't like it.

But then the respondents won't know who/what they're responding to, which could lead to problems.  I'll take suggestions on this; post an ISO under alias or regular handle even if what's looked for is extremely out of character for the usual persona?

local regional board, just don't put your link on the post.  Or you could post on your local ad board and see what happens...

Be careful how you do it though because if it looks like an ad, it will get pulled. If it appears you are seeking clients, it will get pulled. So word it as an ISO, much like a guy would, then when they contact you... you can work out the details. (via pms or them going to your profile and using the contact information from your websites/ads)

Alias would have more defensibility against being an ad, but regular would mean that hobbyists would know who they were responding to and be able to gauge by their tastes. There's nothing worse than a chemistry and preference mismatch!

I wouldn't respond to an alias in that situation, no telling if you were a provider legitimately seeking certain guys or a guy posting a jacked up thread just to see what happens.

I agree with the other respondent that you should use your regular handle.  I give you credit for taking a different approach, but why not put this information in your ad?