Perhaps glue together sound-proofing panels around your piano to make a sound-proof "practice box", I would like that.
Can you really practice in a piano store? It would be wierd, bringing all my music, metrnome, doing exercizes and scales, ignoring the wandering customers, the loud-mouthed salespersons, the five year old playing "Ode to Joy" with one finger, they would throw you out sooner or later anyway.