Once upon a time, a young, naive engineer thought it would be a good idea to separate out some of the functionality for his app into a COM component, written in C#. Visual
I know this is an older question, but others may find this useful...
After struggling with this myself, I found that you can capture the type library information by using tlbexp.exe then heat both the dll and the tlb file. Include the outputs of both of those in your wix project and you should be good to go.
tlbexp.exe dllFile.dll /out:dllFile.tlb
heat.exe dllFile.dll ...
heat.exe dllFile.tlb ...