Call Windows Runtime Classes from PowerShell - window 8 Lockscreen Switcher

I'm trying to make a what I thought would be a simple script to pick a random file from a given directory and set it as the lock-screen image on windows 8. Unfortunately it doesn't look like windows exposes anything directly to powershell to touch the lockscreen. I started out with this question from Stack overflow, call-windows-runtime-classes-from-powershell which looked like he started with the same end goal as I have, but the thread doesn't go into how to actually set the image.

With a little more searching I found this link How to change Lockscreen using JS in win8 app which got me started down the right path I also found examples for Javascript, C#, C++, and VB on msdn on how to change the lockscreen but I just can't quite figure out how to implement in Powershell.

Picking a random image is trivial:

$wallpaper = Get-ChildItem $Path2wallpaper
$NewWPimage = $wallpaper[(Get-Random -Maximum ($wallpaper.count))].FullName

What I'm stuck on is how to actually set the image. Looking at everything I could find I think the code below should work if I knew how to convert $NewWPimage to a .Net stream?

[Windows.System.UserProfile,Windows.System.UserProfile,ContentType=WindowsRuntime]
[Windows.System.UserProfile.LockScreen]::SetImageStreamAsync($img1)

If someone could explain better to me how to work with these .Net objects, or at least the code needed to go from having a file path (ie c:\users\UserName\Wallpapers\newImage.jpg) to setting that file as the lockscreen That would be so awesome. Sorry My programing terminology is pretty week so please forgive me if I'm using the wrong terms.

Solution

Judging from the Lack of Responses it looks like working with WinRT Classes must be hard. However I did find a different way to programmatically change the Lock screen in windows 8 using powershell.

Thanks to Will over on powershell.org I found out that in windows 8/8.1 there is a user Level Lock screen and a system level lock screen. The system level lock screen image can be set in a registry key, and the User level lock screen can be disabled with a registry key, which leaves the system Lockscreen to be the global lock screen. Check out eightforums.com for more details.

So here is the code that I worked out for setting a random lock-screen.

$wallpaper = Get-ChildItem $Path2wallpaper
$NewWPimage = $wallpaper[(Get-Random -Maximum ($wallpaper.count))].FullName
$RegPath = "HKLM:\SOFTWARE\Policies\Microsoft\Windows\Personalization"
if (Test-Path -Path $RegPath)
{
    Set-ItemProperty -Path $RegPath -Name LockScreenImage -Value $NewWPimage
}
else
{
    New-Item -Path $RegPath -Type Directory
    New-ItemProperty -Path $RegPath -Name NoChangingLockScreen -PropertyType DWORD -Value 1
    New-ItemProperty -Path $RegPath -Name LockScreenImage -PropertyType String -Value     $NewWPimage
}