Recording channel 1 and 2 separately on my RX2

Hi! I wonder how I can record my Dj mixtape on my XDJ-RX2 so that I get channel 1 and 2 recorded separately and not in 1 file (that is what happens when I use the USB Rec button on the RX2) Cause I want to be able to edit afterwords and adjust volume levels and etc :)