let's have #include "umock_end_mocks.h" and #include "umock_begin_mocks.h"

Those 2 headers would contain

#define ENABLE_MOCKS

respectively
#undef ENABLE_MOCKS
#include "umock_c/umock_c_prod.h"

and should have a mechanism where 
1. "umock_begin_mocks.h" after "umock_begin_mocks.h" is error
2. "umock_end_mocks.h" without "umock_begin_mocks.h" is error
3.  "umock_end_mocks.h" after "umock_end_mocks.h" is error
