just don't look for external reference assemblies at all...

why is this so hard and undocumented

Author: al2me6

KSPCommon.props

@@ -104,6 +104,18 @@
     <DebugType>portable</DebugType>
   </PropertyGroup>
 
+  <!-- Prevent the compiler from acquiring or referencing any external reference assemblies -->
+  <PropertyGroup>
+    <!-- Do not download the .NET Framework Target Pack NuGet package automatically -->
+    <DisableTransitiveFrameworkReferenceDownloads>true</DisableTransitiveFrameworkReferenceDownloads>
+    <!-- Instruct the compiler to not automatically reference mscorlib -->
+    <NoStandardLib>true</NoStandardLib>
+    <!-- Prevent the GetReferenceAssemblyPaths task in Microsoft.Common.CurrentVersion.targets
+         from attempting to locate an external copy of the reference assemblies. -->
+    <AutomaticallyUseReferenceAssemblyPackages>false</AutomaticallyUseReferenceAssemblyPackages>
+    <FrameworkPathOverride>$(ManagedPath)</FrameworkPathOverride>
+  </PropertyGroup>
+
   <!--Import references-->
   <ItemGroup>
     <Reference Include="$(ManagedPath)\System.dll">