I have a large Simulink model that contains numerous subsystems and model references. The way my model works is that it modifies a large struct type (defined as a Simulink Bus) in place as it passes through components of my model. I am using this model to produce production C++ code using Embedded Coder. Given the scale of my model, and the large memory footprint of the struct type, I do not want reusable functions in my code which copies the struct to a new buffer for output. I want the function to optimize its buffer usage by modifying one struct variable in place. 
This would effectively change the function signature for my reusable function from something like:

void exampleFunction(structType *structIn, structType *structOut) { ... }
to something like: 

void exampleFunction(structType *structInAndOut) { ... }
where one argument is modified in place and treated as output. 
I have done this with Model References in my model.
Is this possible for reusable functions of a subsystem?