geant4-config should provide an option for static library usage. It does not at present output needed external libraries for static builds.
First step is to just add an option(s) to determine if the install of Geant4 has static/shared libraries available. Having a "--static" option may need full paths to be emitted, and may be compiler dependent. Review for 9.6, otherwise leave to next release.
Marking as LATER because the chain of dependencies and getting correct order is complicated and needs careful thought.