As you can see in the datasheet, the high-current pins are mapped to multiple pads on the footprint. I am trying to figure out how to do this in Altium, but the proper approach isn't clear. I have also come across various forum posts claiming it is impossible up until at least 2018... is this still true? I was under the impression that Altium is the industry standard software, so I would be a bit shocked if it truly lacked this kind of basic functionality.
Instead of assigning the correspondence on the footprint/component library, you can just connect them by wire in the schematic side, which seems a more realistic approach, once you are connecting them outside the chip, not internally - although all them belongs to the same input.