It was a good idea. Let him see how it should be done. How he could do it.
Without a head, Snape nodded. Without an arm, he reached out. Without a hand or a wand, he gestured, beckoning. Grasping the cup with his magic, his self, a grip surer and purer than mere flesh could ever achieve.
Here, in the depths of his mind, even incantations were not necessary. Instead, he simply thought, Fly.
The cup lifted, light as a downy owlet's feather, as a starburst of thistledown. It soared, darted here and there, hovering, deft and effortless as a hummingbird.
Snape did his best to override his instinctive inclination to secrecy and lay his mind wide open. Did his damnedest to let Al feel the perfect silence of his focus, as utterly untroubled by extraneous physical stimuli as if he was a disembodied spirit.
There. This is how it should be. This is how it can be, for you.