If I understand correctly, you would like to incorporate C code generated from one model into another model via a wrapper S-function. This is, in principle, possible, and should be release independent.
In order to build this wrapper, be sure to include all of the generated header files and helper functions produced by the Simulink code generation process. You can use the Legacy Code Tool to do this. Documentation on Legacy Code Tool can be found at the link below, or by searching "Legacy Code Tool" within the documentation of your installed MATLAB release.