You could certainly add another target and add REFERENCES to the files for the unit tests. They may more may not need modification of the module import names. A file may be referenced in multiple projects, and this could even be automated, as there are tools such as PBXProj for python to allow reading/writing of the Xcode project.
Alternatively, but I am not sure, it may be possible to create an aggregate target with the other items added - this is just speculation.
Perhaps a better question is why can't multiple test targets be run? Surely a script or fast lane could help?