How to save fingerprints and restore them after full wipe?

Ok, so this is the issue:
I flash ROMs all the time.
I want to connect my phone to my work email, which forces me to use a PIN to unlock. I can also use a fingerprint instead to unlock.
Since my girlfriend uses my phone from time to time, I don't want to make her add her fingerprints everytime I do a full wipe.
(why full wipe? to test other ROMs for example)

Is there a way to keep the fingerprints backed up somewhere?
thanks.