To get RD only on a Di2 system all you need to do is not fit a front derailleur.
If you want to, the shifter buttons can be remapped to your heart's content using the standard eTube software.
That's what I thought - because they sell the single button shifters, it can't be that tricky. My TT bike doesn't have a FD but I left the normal shifter and cable in place in case I decide to go back to 2x.
@hippy started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
To get RD only on a Di2 system all you need to do is not fit a front derailleur.
If you want to, the shifter buttons can be remapped to your heart's content using the standard eTube software.