To do this you would need to input a System Exclusive message in your sequencer track and allow approximately 50-100ms for the ‘Rack to recall the setup

F0 43 10 6F 0A 00 01 03 F7 – This will select USER MULTI mode
F0 43 10 6F 0A 00 01 00 F7 – This will select VOICE mode

Sidenote:When working with an external sequencer there is really no advantage to working in VOICE mode, as you can call up any VOICE you need while working in MULTI mode.