Yes it is possible and works.
1) check that the pins match on the adapter and the media.
2) Update the BIOS before revision F6a https://www.gigabyte.com/MicroSite/462/images/BIOS-Z270P-D3.zip
3) Set some setting in the BIOS
...
4) Enjoy of working 7 GPUs
1) check that the pins match on the adapter and the media.
2) Update the BIOS before revision F6a https://www.gigabyte.com/MicroSite/462/images/BIOS-Z270P-D3.zip
3) Set some setting in the BIOS
...
4) Enjoy of working 7 GPUs

Everything is working fine, thx for sharing. 7x1070ti successfully mining.