As a designer, sometimes you see something that makes you bury your head in your hands and say, "SHIT! Why didn't I think of that?" This is one of those times.
The die cut, plus the cassette tape card holder?
This is called "killing it"
I can't believe Grandmaster Flash, Kid Capri or Funk Master Flex don't have something like this design for their cards.
Kiss My Black Ads and Adgoodness for finding it.