Andreas is right. Shortcuts can be used to run arbitrary MATLAB code, but not map to other Toolstrip buttons.
You can also add any item from the Toolstrip to the quick access toolbar, which is (by default) just next to the search box at the top right of the desktop. You can make the toolbar wider by moving it below the Toolstrip.
Most users we have worked with have found this to be a nice way to have a custom environment with easy access to the controls you need most often.