I would say the best place is in the scheduler. The schedulers are to be found in the “+schedulers” directory. Which .m file is relevant for you depends on the selected scheduler, e.g., propFairSunScheduler.m if you have selected proportional fair.
In the scheduling object, you could simply assign to RBs to any users in ABS. Of course you would first have to figure out whether the scheduler belongs to a macro or a femto.