open the radial menu on the projector, select insert data cube, dont hit ok.
trade away the data cube.
choose the data cube you just traded away, and hit ok to load it.
the disk will load into your projector and will disappear from the other persons inventory.
seems to work as long as theyre on the same planet, but still works even if they log off. im thinking you could trade to a friend, he could sell, and you could yoink it from the buyers inventory... but i havent tested trading the data cube a second time and snatching it.