Code generation - export signals as struct

I encapsulate my signals (and parameters) in structures. Currently I am able to do this defining my signals with a Storage Class "Struct(Custom)". This yelds the following code

in my_model.c file

my_signal_struct_type my_signals;

in my_model_types.h file:

     /* Type definition for custom storage class: Struct */
      typedef struct my_signal_struct_tag {
         real_T u1;
         real_T u2;
         real_T u3;
       } my_signal_struct_type;

Now I am in the need to export these definitions and declarations to files that can be shared. I see that it is possible to declare my signals of type mpt.Signal and use the Storage Class "ExportToFile(Custom)", like this my signals are defined in a separated C and H files.. and that is exactly what I need!!! Well, alsmost exactly, the problem is that every signal is declared as a stand alone variable. I need them to be part of a structure.

I believe that I need to create my own custom storage class and modify the MPTUnstructured.tlc file, but i don't know how to start.