Accessing Contact Forces in a New Compute

I'm trying to write a new compute script to throw in the src folder that sums up the magnitude of the contact forces in the system. I tried to basically copy compute_pair_gran_local.cpp since that file directly works with the contact forces, and in my new file I would put a compute_scalar command to output a single global value that I want. The problem I run into is that compute_pair_gran_local.cpp only allows a single simulation to have one PairGran object registered using the register_compute_pair_gran_local function. So basically it seems that if I make a script that accesses the same information in compute_pair_gran_local.cpp then I will get an error or LIGGGHTS will crash.

Is there a simple way to access an array of all the contact forces using pointers? Or is there a series of steps to take in the C++ file to ultimately get this type of array? Is it also possible to have a compute_scalar() function in compute_pair_gran_local.cpp that works simultaneously with compute_local() so that I can have the scalar I need without sacrificing the outputted array of contact force information?