Azure – PowerShell create new Azure VM from uploaded disk (not image)

I have a VHD in Azure storage. That VHD is configured as an OS disk through a command like the following:

Add-AzureDisk -DiskName $newCode -MediaLocation "http://$script:accountName.blob.core.windows.net/$newCode/$sourceVhdName.vhd" `
    -Label $newCode -OS "Windows"

I would like to create a new VM pointing at that disk. From what I can tell if I was doing this with an image I would do something like:

New-AzureVMConfig -Name $newCode -InstanceSize $instanceSize `
    -MediaLocation "http://$script:accountName.blob.core.windows.net/$newCode/$sourceVhdName.vhd" -ImageName $newCode  `
    | Add-AzureProvisioningConfig -Windows -Password $adminPassword `
    | New-AzureVM -ServiceName $newCode 

However this is wrong for me because I don't have an image – I have a configured VHD that is not sysprepped and can't be.

How can I create the VM in PowerShell to point at the existing disk like I can through the portal?