Already can - just connect your export USB to the host computer and load tracks from there.
Use recordbox USB for performance section
Please consider to build a way to use USB's from other DJ's created in recordbox for the performance section. If a setup like the DDJ or RX is used for a party (where they are also build for) multiple DJ's should be able to use the same laptop.
also for this case, i was on recordbox 4... For some reason all my issues have been resolved in version 5 so great job in that development...