Pit Optimization Stock Pile Priority

When running a pit optimization period analysis I have setup LG, MG and HG stock piles, the optimizer only starts stock pile reclaim once the mining rate of ore is not enough to feed the plant. So for example in year 3 I might be sending LG directly from Mine to Processing when I have HG sat on the stock pile. The HG stock pile is not reclaimed until later years and after a bunch of LG directly from ROM has been processed in its stead. 

Does anyone know of a way to prioritize the source of the material going to the processing faculity, or is the only way a manual shedule.