How can I generate code for subsystem parameters?

I have some variables in my Simulink model that I wish to generate a separate header and source file for. I was wondering if this is possible with Real Time Workshop Embedded Coder.

Example.

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myheader.h

extern uint32 x;

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myheader.c

uint32 x = 5;

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When I create a variable in the Matlab workspace it generates code in the mymodel.h and mymodel.c files. I still want some of my variables to be generated there, but I also need those mentioned above in separate files and then include the header file and use them in the main model.