So sollte das gehen:
$disk = 'C:'
$script = 'gwmi Win32_LogicalDisk -Computer . -filter "name='''
$script += $disk
$script += '''" |%{$_.name, [math]::truncate($_.freespace/1GB)} | select-string "^(?!.*'
$script += $disk
$script += ')" '
$sb = [scriptblock]::Create($script)
$TEMP = Invoke-Command -ScriptBlock $sb