benmanson.com/review/di2/di2buttons.htm
That's old 5-wire DuraAce 79xx Di2, not new 2-wire CAN-bus E-Tube Di2.
Yes, to do the same with E-Tube you need to use the SW-R600 and fit flying leads to it.
@Brommers started
London Fixed Gear and Single-Speed is a community of fixed gear and single-speed cyclists.
That's old 5-wire DuraAce 79xx Di2, not new 2-wire CAN-bus E-Tube Di2.