Where is AfterBuildCompiler (msbuild) target defined?

I'm trying to get multi-project ASP.NET MVC areas (like described here) working in MVC 3 on .NET 4 (since it's not officially supported since MVC 2 Beta). So i've found Microsoft.Web.Mvc.Build.dll from MVC 2 Preview and modified the script so it can use the assembly directly (it's not strong-named):

<UsingTask TaskName="Microsoft.Web.Mvc.Build.CreateAreaManifest" AssemblyFile="..\..\Microsoft.Web.Mvc.Build.dll" />
<UsingTask TaskName="Microsoft.Web.Mvc.Build.CopyAreaManifests" AssemblyFile="..\..\Microsoft.Web.Mvc.Build.dll" />

But i get "error MSB4057: The target "AfterBuildCompile" does not exist in the project.". Where is this target defined?

Found a lot of related posts but none working. Should i abandon the hope to have multi-project areas or try MVCContrib portable areas as alternative (looks not what i need at first glance)?

You may check the following article.