Using GetRequestStreamAsync and GetResponseAsync in .Net 4.0 Portable Class Library

I've been building a small Portable Class Library and it makes use of the WebRequest class. I'm targeting .Net 4.0 (and above), Silverlight 5 and Windows App Store. I would target the phone as well but it doesn't support the TPL at the moment - WP8 is just around the corner:

I wanted to use async method GetRequestStreamAsync  & GetResponseAsync but these aren't supported in .Net 4.0 and when creating a Portable Class Library you only get the commonly supported methods across the configured platforms - so no support then or may be not...

Why not just create a couple of extension methods?

   1:  public static class HttpWebRequestExtensions

   2:  {

   3:      public static Task<Stream> GetRequestStreamAsync(this HttpWebRequest request)

   4:      {

   5:          var tcs = new TaskCompletionSource<Stream>();

   6:   

   7:          try

   8:          {

   9:              request.BeginGetRequestStream(iar =>

  10:              {

  11:                  try

  12:                  {

  13:                      var response = request.EndGetRequestStream(iar);

  14:                      tcs.SetResult(response);

  15:                  }

  16:                  catch (Exception exc)

  17:                  {

  18:                      tcs.SetException(exc);

  19:                  }

  20:              }, null);

  21:          }

  22:          catch (Exception exc)

  23:          {

  24:              tcs.SetException(exc);

  25:          }

  26:   

  27:          return tcs.Task;

  28:      }

  29:   

  30:      public static Task<HttpWebResponse> GetResponseAsync(this HttpWebRequest request)

  31:      {

  32:          var tcs = new TaskCompletionSource<HttpWebResponse>();

  33:   

  34:          try

  35:          {

  36:              request.BeginGetResponse(iar =>

  37:              {

  38:                  try

  39:                  {

  40:                      var response = (HttpWebResponse)request.EndGetResponse(iar);

  41:                      tcs.SetResult(response);

  42:                  }

  43:                  catch (Exception exc)

  44:                  {

  45:                      tcs.SetException(exc);

  46:                  }

  47:              }, null);

  48:          }

  49:          catch (Exception exc)

  50:          {

  51:              tcs.SetException(exc);

  52:          }

  53:   

  54:          return tcs.Task;

  55:      }

  56:  }

When used with the AsyncBridge NuGet package to provide async support in .Net 4.0 \ Silverlight 5 you get exactly the same syntax as if this was a standard .Net 4.5 library: