function Convert-XAMLtoWindow
{
  param
  (
    [Parameter(Mandatory=$true)]
    [string]
    $XAML,

    [string[]]
    $NamedElements,

    [switch]
    $PassThru
  )

  Add-Type -AssemblyName PresentationFramework

  $reader = [System.XML.XMLReader]::Create([System.IO.StringReader]$XAML)
  $result = [System.Windows.Markup.XAMLReader]::Load($reader)
  foreach($Name in $NamedElements)
  {
    $result | Add-Member NoteProperty -Name $Name -Value $result.FindName($Name) -Force
  }

  if ($PassThru)
  {
    $result
  }
  else
  {
    $result.ShowDialog()
  }
}

$xaml = @'
<Window
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   MinHeight="350"
   Width="525"
   SizeToContent="Height"
   Title="PowerShell WPF Window"
   Topmost="True">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="30*"/>
            <ColumnDefinition Width="30*"/>
            <ColumnDefinition Width="30*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="20*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="20*"/>
        </Grid.RowDefinitions>
        <Button
         Name="SEP"
         Width="80"
         Height="25"
         HorizontalAlignment="Right"
         Margin="0,0,82.667,125"
         VerticalAlignment="Bottom">SEP
        </Button>
    </Grid>
</Window>
'@

$window = Convert-XAMLtoWindow -XAML $xaml -NamedElements 'SEP' -PassThru


$window.SEP.add_Click(
  {
    [System.Object]$sender = $args[0]
    [System.Windows.RoutedEventArgs]$e = $args[1]

  }
)


$window.ShowDialog()