I'm a bit late to this thread, but ...
I've seen advertised a music stand, similar to the standard type used by string/brass/woodwind players. But ... instead of resting atop a post, it's cantilevered on a horizontal arm. Its floor-stand could be placed behind or beside the piano, with the arm reaching over to an appropriate position in front of the player.
[This might work with a smaller upright (spinet, studio) but not with the taller, full-size uprights.]