Simple shelf puzzle?

[Damascus]

I actually do something fairly similar in my custom story. I just took a shelf and turned it into a Push object with high mass (like 30). Just by itself, the Player can tip it over, but when I put enough books on it, it actually adds enough weight to keep the player from moving it. No scripts needed!

Keep in mind, though, that the shelf will most likely just fall over instead of sliding upright.