The way I see it you'd not 'actually' be rotating it, rather just scrubbing backwards and forwards through frames of an animation of it rotating. The trick would be to sync similar animations of the clothing to match the mannequin. Plus of course the hassle of having to render out all those animations (with alpha channels/masks), importing them into flash etc.

As far as actually setting the actionscript for this, I'm afraid you'll have to wait for one of the flash guru's to pop there head round the corner