Lenovo finally released a BIOS update for the Yoga 900 13ISK2 that creates an AHCI SATA Controller Mode selection to allow for the installation of Linux!
Lenovo dowload page
Direct update link
However, when I run the flashing application I get the error:
'The version of ROM file is not newer than that of BIOS'
Following the advise given here, I extracted the contents of the BIOS update file provided by Lenovo and changed the
setting in line 457 from
Then running the H2OFFT-W executable opened the BIOS flashing utility and I was able to succesfully make the update!