You use zero width wires on the Dimension layer to specify the outline. You can use the Miter tool to make the curves.
Generally speaking, you'd rough out the outline using straight lines of the correct lengths as specified by the datasheet. Then you'd use the miter tool to add the correct radius to each line.
You can also stick the outline in a custom component to make it easier to re-use. In that case you'd delete the default outline when you make the new board, then add the custom component instead.
And don't forget to print it out and check the actual physical fit before you spend a bunch of time laying out the board