Now thats a clever idea!
Yes, definitely possible. Most systems an have different materials, for example one "real" ABS building material, and one blank material to fill and support hollow parts or overhangs.
In this case you could not remove the inner fill material, but that wouldn't be a problem anyway.

I like this idea.
However, you could make a similar token by laminating the key between different sheets of paper/plastic, maybe with a hologram or the like as secure top layer? Or something like a scratch card?
..For all the people who don't have a 3D printer yet, anyway.

Ente