The simple technique (i.e. sendMessage + notifyUserMessage + Metadata/Data Adapter communication) is also available with Remote .NET Data Adapters.
You should code your Metadata Adapter as a Remote .NET Adapter too ("NotifyUserMessage" is still provided by the .NET library interface).
Then you can have your Remote Metadata and Data Adapter talk to each other quite easily by loading them in the same Remote Server instance. This is shown in DOCS-SDKs\sdk_adapter_dotnet; see chapter 1.6 in doc\DotNet Adapters.pdf. The sample code shows loading both adapters, though communication between them is not covered.

The full technique (i.e. an intermediate servlet and a message bus) is entirely played outside Lightstreamer. We use it in the PortfolioDemo; see http://www.lightstreamer.com/portfolioDemo.htm, where some raw code is available for the java case.