• Cygwin SSHD installed and setup
• backuppc local/domain account with admin privileges (for taking VSC)

Specifically you do have to use a password, once. Create a Scheduled task logged in on the Windows server as the backuppc user (the user that you'll be logging into the sshd with) - should probably be a service account. Scheduled task will c:\cygwin64\bin\bash.exe the bash script that does the stuff, including the VBS that creates the VSC

It will work without a password!

scheduledtask.xml

<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.2" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
  <RegistrationInfo>
    <Date>2015-06-05T07:29:03.7810614</Date>
    <Author>DOMAIN\backuppc</Author>
    <Description>Create and mount Volume Shadow Copy for BackupPC</Description>
  </RegistrationInfo>
  <Triggers>
    <TimeTrigger>
      <StartBoundary>1980-01-01T00:00:00</StartBoundary>
      <Enabled>true</Enabled>
    </TimeTrigger>
  </Triggers>
  <Principals>
    <Principal id="Author">
      <UserId>DOMAIN\backuppc</UserId>
      <LogonType>Password</LogonType>
      <RunLevel>HighestAvailable</RunLevel>
    </Principal>
  </Principals>
  <Settings>
    <MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
    <DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
    <StopIfGoingOnBatteries>false</StopIfGoingOnBatteries>
    <AllowHardTerminate>true</AllowHardTerminate>
    <StartWhenAvailable>false</StartWhenAvailable>
    <RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
    <IdleSettings>
      <StopOnIdleEnd>true</StopOnIdleEnd>
      <RestartOnIdle>false</RestartOnIdle>
    </IdleSettings>
    <AllowStartOnDemand>true</AllowStartOnDemand>
    <Enabled>true</Enabled>
    <Hidden>false</Hidden>
    <RunOnlyIfIdle>false</RunOnlyIfIdle>
    <WakeToRun>false</WakeToRun>
    <ExecutionTimeLimit>PT8H</ExecutionTimeLimit>
    <Priority>7</Priority>
  </Settings>
  <Actions Context="Author">
    <Exec>
      <Command>c:\cygwin64\bin\bash.exe</Command>
      <Arguments>--login -c "/cygdrive/c/vscbackup/pre_backup.sh"</Arguments>
      <WorkingDirectory>c:\vscbackup</WorkingDirectory>
    </Exec>
  </Actions>
</Task>