Following Brandon Linton's post about creating and importing a WinPE 3.1 boot image for use in ConfigMgr 2012 SP1 CU2, below is a little Powershell script to enable command-shell
#CM2012
R2 - Enable Command-Shell in WinPE 3.1 Boot Image
#Replace below OSDxxxxx with your boot image package ID
$BootImagePackageID = "OSDxxxxx"
#Get the
Boot image - Replace OSD by your site code
$BootImageQuery = Get-WmiObject
-Namespace "Root\SMS\Site_OSD" -Class SMS_BootImagePackage -Filter "PackageID='$BootImagePackageID'"
#Read
Properties
$BootImageQuery.Get()
#Enable
Command-Shell
$BootImageQuery.EnableLabShell = 'True'
$BootImageQuery.Put()
#Update
Distribution Points
$BootImageQuery.RefreshPkgSource()
