I have wanted to do something similar to efficiently dispose of my child's toys. Step 1: I put a red sticker on any toy I don't think has been played with in a while. Step 2: three weeks later, if the sticker is still there then I take the toy and put it in a holding pen. Step 3: if the child has not noticed it was missing three weeks later, the toy can be recycled/donated.

We haven't done this yet, but it's on our list of things to try.