Marshaling javascript dictionaries to Silverlight

Question

I have had not trouble passing primitive values from Javascript to Silverlight through the HTML bridge, but I keep getting stuck when trying to pass a Dictionary. Furthermore, I can't find a single sample of this working anywhere online, though the MSDN documentation says it should just happen automatically. Instead, I get an error that the type cannot be converted to a Dictionary.

Here's the javascript code:

mapPlugin = null;
function pluginLoaded(sender) {
   var mapPluginObject = $find("<%=silver.ClientID%>");
   mapPlugin = mapPluginObject.get_element();
}

function Proxy() {
   var dict = {};
   dict['Color'] = 2;
   dict['Foo'] = 'Bar';
   slPlugin.Content.DataSeriesManager.Scriptable(dict);
}

...

 <asp:Silverlight ID="silver" runat="server" Source="~/ClientBin/silver.xap"
        MinimumVersion="2.0.31005.0" OnPluginLoaded="pluginLoaded" Width="100%" Height="100%" />

Then on the C# / Silverlight side, I have:

private void Application_Startup(object sender, StartupEventArgs e)
{
   Page page = new Page();
   HtmlPage.RegisterScriptableObject("DataSeriesManager", page.DataSeriesManager);
   this.RootVisual = page;
}

[ScriptableType]
public class DataSeriesManager
{
   [ScriptableMember]
   public void Scriptable(Dictionary<string, object> dict)
   {
      // ...
   }
}

Thanks,
-Scott