Run Powershell script on startup before user log on

I have a PowerShell script which I used to add machine to a domain.  The purpose is to allow me to snap a VM to a clean state, before machine has been added to a domain.

I would like to be able to setup the snapshot of the VM so that when it starts up, it automatically runs the PowerShell script.
I tried populating the following registry key, but this only works after user logs on.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce

I then tried the following registry key, but nothing seems to happen:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServicesOnce

I also tried creating a scheduled task to call the script, and configured the task to run on start up, but nothing happen.

I think with the last two approach, the script is getting called too early, before a required service is loaded.

I know the script works, because it works when I call it on command line, and it works when I use the log on method (RunOnce) registry key.
Here's the PowerShell script:

$domainName="mydomain"
$domainPw="mypassword"
$domainAcc=$domainName + "\MyAdminUserName"

$comp = get-wmiobject Win32_ComputerSystem
$comp.JoinDomainOrWorkGroup($domainName,$domainPw,$domainAcc,$null,3)

$reboot = (gwmi -Class Win32_OperatingSystem)
$reboot.psbase.scope.options.enableprivileges = $true
$reboot.reboot()

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Here's the DOS script which is used to call the PowerShell script:

rem schtasks /Delete /TN AddMachineToTestlabDomain
rem Above is only needed when using task schedule method
powershell Set-ExecutionPolicy RemoteSigned
powershell c:\AddMachineToTestlabDomain.ps1

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Does anyone know how I can configure Windows 2008 machine to automatically get added to a domain on bootup without requiring user to log on?
Or how to call above script on bootup without requiring user to log on?