Ok seems to work if I use pin 1 on the power dock to connect the data line.
There may be restrictions on which pins you can use as GPIOs; this gave a hint:
By default, the Serial, SPI, and I2C pins implement these communication protocols and cannot be used as GPIOs. Similarly, the I2S and PWM pins are set to GPIO mode by default.
So I see on the expansion header (different pinout than the power dock) that pins 0 and 1 are associated with I2S so I used pin 1 and that was successful.
root@Omega-0B45:~# insmod w1-gpio-custom bus0=0,1,0
root@Omega-0B45:~# cd /sys/bus/w1/devices/
root@Omega-0B45:/sys/bus/w1/devices# cd 28-041671215aff/
root@Omega-0B45:/sys/devices/w1_bus_master1/28-041671215aff# cat w1_slave
47 01 4b 46 7f ff 0c 10 6c : crc=6c YES
47 01 4b 46 7f ff 0c 10 6c t=20437