Downhill Assist Control DAC system activation

Almost all mid and top of the line 2015 Toyota Highlander cars have Downhill Assist Control DAC system. But, for some reason, not the top of the top of the line. We bought the Platinum version of the 2015 Highlander Hybrid and noticed that the DAC feature was removed, even though there is a space under the dash for another button, and the intelligent cruise control and traction control are already activated. Nevertheless, I really want to add the DAC to our car as we live among steep rolling hills with snow and ice in the wintertime and every year, we find ourselves kicking ourselves for not having this feature to slowly traverse the tricky slippery areas. Is it possible to add it now to our car? Please help! Thanks!