Rear Camera Mirror (RCM) Camera Selection

[MCM3M]

I have the 2019 Sierra Denali which has the Rear Camera Mirror (RCM). My issue is that the camera used for this view is located above the window on the rear of the cab. The problem with this is that if my rear view is blocked by cargo in the rear it also blocks the view of the camera being used  making the view useless. In my case, a much better view would be achieved if the backup camera located on the tailgate could be used. Does anyone know of a way to accomplish this?