For every check in we get generate a new build environment, so managing a history file would have been quite difficult.

What about checking the history file into its own rep? Clone it as part of the build-environment setup, and commit/push after validation. You can even use this across a group of people and share each other's mutations.

Or even simpler, why not have build actions copy it to/from a specific location outside the build target dir? You could even make it a shared network drive, if you didn't care about the possibility of losing someone's changes if two people run tests at the same time.