MartinL:
Hi robot9,Yes it's possible to create a second I2C channel, using one of the SAMD21's spare SERCOM (Serial Communication) modules.
It's detailed in this Adafruit tutorial: Creating a new Wire | Using ATSAMD21 SERCOM for more SPI, I2C and Serial ports | Adafruit Learning System.
The Tutorial you referenced is for Adafruit Feather which is a different variant from the Arduino Zero.
You are assuming that on the Arduino Zero the extra I2C pins are brought out to board pins.
As far as I know the Arduino Due is the only board with more than one i2c channel.
I have done some more checking and the below tutorial may be what you need to pursue.
https://www.arduino.cc/en/Tutorial/SamdSercom
I have not attempted it. I may have to try it in the future.