This can be done through WMI. I have the exact same issues, and found that you can look at this WMI class to find out if the SuperVisor password is set.
Get-WmiObject -Class Lenovo_BiosPasswordSettings -Namespace "root\wmi"
If Password state is 0, it is not set, and if it is 2 it is set. (I have not been able to find any documentation on possible values, so there might be more)
You can only change password on machines that have had a password set manually, (To prevent malicious users from locking down, all your machines without knowing a password)