The simplest way to flash/upgrade the X102BA BIOS does not need any particular operating system installed.
Fetch your new BIOS from http://support.asus.com/download.aspx?SLanguage=en&p=3&s=533&m=X102BA.
Unzip the .ZIP file to a FAT formatted USB flash device.
Insert the USB flash device and boot to the BIOS (by tapping escape as you power on and selecting “enter setup”).
Pick “start easy flash” from the “advanced” menu in the BIOS.
Select the file, press enter, and the flash process will start.
At the time of writing, the newest available on the Asus site was version 214, which confusingly is labelled both “214” and “2.15.1236” inside the BIOS. My X102BA shipped with 212. Note “Version” string near top of screen, and different number on bottom line: