In the Reef forum you asked about doing this with a pleco....sorry but the answer is still no. It would be nice if you could, because they sure would take care of any algae problem you might have, but the poor fish wouldn't last very long that way..........
Ive done it wiht a beta, and my friend did it with mollies, i just very slowly added salt, i never got the beta to the exact saltanity level (it jumped out of the tank in the night and dried up) but it was just under 1.000 im sure he would of lived.
It can be done with mollies. I purchased 6 mollies to cycle my 55gal. Over an 8 hr period i slowly added water from my tank (1.023 sal.). After that i just placed them in my tank and used the to cycle it. Well its 2 months later, the cycle has been long completed and two of them had babies( 9 total). I have added several fish including a yellow tang and rarely are the mollies picked on. Soon i will be swaping them out at my LFS. It can be done at least with mollies. Good luck.
In my experience it can be done with black mollies and guppies. You can keep them even after your tank is ready for others. It's a good food source for your anamone and other fish as time passes.