Found a work around of sorts.
- start an Admin command prompt (cmd.exe) and change directory to wherever you’ve saved the installer.
- change the following environment variables to start with the drive letter you want ( e.g: set=ProgramFile=F:\Program Files )
- Execute the installer by running from this cmd window.
Haven’t fully tested, but it looks like it installed to the right spot now and not defaulted to C:\ drive.