Official comment
Even if there was a MIDI function for it, the DDJ-SB wouldn't be of any use in that scenario... as the hardware itself doesn't have two deck layers, all of the controls on the hardware transmit the same MIDI signal at all times. Even if you switched the decks on screen, the play/pause button on the SB would still be controlling the other deck.
Please consider using a hardware controller with four deck control offering two layers of function.