Here is the code to put in your user .sublime-keymap file:

 { "keys": ["alt+shift+7"],
    "caption": "2 cols (full - 2)",
    "command": "set_layout",
    "args":
        { "cols": [0.0, 0.5, 1.0],
          "rows": [0.0, 0.5, 1.0],
          "cells": [ [0, 0, 1, 2], [0, 1, 2, 1], [1, 1, 2, 2]
        }
},