I added this to a console app
<NuGetRepository Include="file:///Users/JohnMoshakis/Documents/develop/Nancy/build/nuget/" />
<Reference Include="mscorlib" />
<Reference Include="System" />
<Reference Include="System.Data" />
<Reference Include="System.Xml" />
Fire seems to recognize that as a repository, I see this in the build output
-> Task RemObjects.EBuild.Elements.ElementsProcessNuGetReferences started for RemoteConsoleApplication, Echoes.
Registering NuGet Repository 'file:///Users/JohnMoshakis/Documents/develop/Nancy/build/nuget/'
E: Package Nancy matching version [2.0.10] was not found in any repositories.
The version number should be ok because I registered the same folder with visual studio for mac and that picks it up.