Tweaking the elevation of a floor tile with an object on it moves the floor, but not the object. Interestingly, this would allow for someone using both constrainfloorelevation and moveobjects to raise a floor to the height of a window frame, place an object on this raised tile edge, then lower the tile back to floor level and leave the object floating, but seemingly resting on the window sill.
As for the artist's conundrum, I would say it is going to depend on how big a room you are talking about making. As an example of what I might do:
11 tile wide room - 2 window tiles, v-shaped cut out into the room with a painting on each side of the v (2 tiles across total), 3 tiles of window, another v, last 2 tiles of window. Depth of the room from there will depend on furnishing and other available space.
Further use of the moveobjects and constrainfloorelevation cheats: multiple paintings on the same wall tile, at different heights. Lower the floor a satisfactory distance, place painting #1. Return the floor to its default height, or higher if necessary, place painting #2. Double dipping on wall space, as it were.