Or, if you don't play a challenge with rules that won't allow you, you could:
- Save you game first before doing anything
- Then put the sculpture base on the lawn
- Save/copy the family to the library (without the sculpture base)
- Go back into the house where the family also still is
- Move the sculpture base into the inventory / family inventory
- Move the family (including the sculpture base in the inventory) out of the house and delete them
- Move the family from the library (the ones without the sculpture base) into the house.
This is just a thought. Not sure if it works, but I think it could. Good luck with it!