I don't know how I missed this for several years, but I discovered when creating a route in HomePort, instead of having to move the pointer to the edge of the screen to move the map, you can just use the arrow keys on your keyboard.
What seems strange though, is if you have zoomed in or out, you have to move the map once with the pointer. After that, the arrow keys work.
Note: This is not something I seriously tested so it's just my first impression. Still, using the arrow keys makes it much easier to move the map if you're creating long routes at a high zoom level such as on the AICW.