This never occurred to me, but it makes perfect sense as an alternate controller for modular perfromances. The CDJ is communicating with the modular synth in the background via control voltages that were burned onto CD. This should be fairly easy to setup with Traktor, S2, X1, or F1 as the control interface and should produce some really fun and bizarre sounds.
And with vinyl as well:
Check out this Muff Wiggler thread for more information about the process.