Install ILMerge from NuGet Set assembly name to "Blah.original.dll"
Set Post-build event command line to:
"$(SolutionDir)packages\ilmerge.2.13.0307\ilmerge.exe" /keyfile:"$(SolutionDir)Key.snk" /out:"$(TargetDir)$(ProjectName).dll" "$(TargetPath)" "$(SolutionDir)lib\foo.dll" "$(SolutionDir)lib\bar.dll"
This will generate a "Blah.dll" with foo.dll and bar.dll merged into it.