This is a great idea!
Couple of thoughts from me though - I noticed that you mention that the part needed to be pressed in, but mine was very loose. I printed at 100% so imagine that the Altoids tin must be different? Not to worry, I stuck a bit of double sided tape on the bottom and it's good and stuck. Second, I think it would be cool if the bits stayed put somehow - I thought a part to stick in the lid that covers them or even a few magnet holes that keep them in place. I'll try to do a remix if I get a minute. (unless you beat me to it)
If you haven't already, add #gift #giftidea to your post, as this will make a great present!
