How can I get my .NET assembly dll to load renamed third-party assembly dlls?

My .NET Assembly DLL loads third-party .NET assembly DLLs. I'd like to rename those third-party DLL files to hide their origin from casual inspection.

I know that if I write a .NET Assembly EXE then I could use an app.config file and specifically the codeBase hint to specify that a required Assembly lives in a renamed DLL file.

But when I define an app.config file for my Assembly DLL I get a run-time Exception specifying the name of the assembly, and it doesn't recognise that the required Assembly is in a renamed DLL file:

System.IO.FileNotFoundException
  HResult=0x80070002
  Message=Could not load file or assembly

My question is - what would I put in the app.config for my .NET assembly DLL so that it can load and use renamed third-party assembly DLL files?