How to merge managed and unmanaged dll into one dll

Question

How to merge managed and unmanaged dll into one dll? I want to merge two dlls in a single one. One is a c# managed dll, the other is a wrapped c++ managed dll with unmanaged c++ code. I have used ILMerge but it does not support unmanaged dll. And I have tested another commercial tool "Salamander .NET Linker", it does not support the unmanaged dll either. Someone even told me that it is not possible to merge managed and unmanged dll into one dll. Does anyboby know how to do this? Any advices are appreciated.