How can I create an empty/dummy/reference AnyCPU DLL (re: lib folder) from x86 and x64 specific DLLs?

[sofakng]

I'm trying to create a NuGet package from precompiled .NET Framework DLLs. However, the DLLs are provided for x86 and x64 but not AnyCPU.

If I understand correctly, I need an AnyCPU DLL for compile-time (lib folder) and I don't need this to be architecture specific, right?

Can I create an empty/dummy/reference lib DLL from either of the x86/x64 DLLs? Is this the best practice?

(the runtime DLLs are placed into /runtimes/win-{86/64}/lib/net40, which I think is correct?)