I am a bigger-bodied skater, so I struggle with this too.
A lot of people have trouble dissociating the shoulders and hips when rotating because of mobility restrictions (usually in the torso or hips or both). I personally deal with this on tailslides too - I am always torquing out of frontside tailslides and going to fakie, and I have to concentrate pretty hard to take them to regular. As far as tailslide-specific "cues" go, I try to open my shoulders a little earlier so my hips have some room to follow through, then I anticipate the turn back to regular as soon as my tail/baseplate locks into the ledge.
One drill that can help with torso and hip mobility is the "World's Greatest Stretch" (video below). This drill encourages a lot of rotation in the torso, and the lunge component can help lengthen tight hip flexors/thigh muscles that affect hip mobility and your ability to rotate.