Is there a means NOT to put the database password in plain text

No.

And … please, suggest away, but there’s no way to do it.

Secure File Permissions Matter

WordPress, like all other web applications, must store database connection info in clear text. Encrypting credentials doesn’t matter because the keys have to be stored where the web server can read them in order to decrypt the data. If a malicious user has access to the file system — like they appeared to have in this case — it is trivial to obtain the keys and decrypt the information. When you leave the keys to the door in the lock, does it help to lock the door?”