Dual sim G4 - how to set up a different ring tone for each sim card?

I have the dual sim version of the XT1622 - 2 GB RAM / 16 GB ROM and am trying to set up a different ring tone for each SIM card. Having gone through the settings several times, I cannot see anywhere on the phone where I can do this. When I go in to "Settings - Sound & Notification - Phone ringtone" and add a ring tone, it is the same ring tone for both sim cards.
My main reason for getting this phone was that I could use it for my personal phone and also for work. It would be very useful to have two different ring tones.

I would appreciate any help in setting this up.
Pat