Set up a second computer, mindlessly spam your range attack hotkey on the other computer. You still have to spam a hotkey, however you are then able to focus all your attention on the other character.
Also I'm pretty sure there are applications/settings/options to mimic 1 keyboards input across multiple apps. You could even do this just for particular keys. For example, hitting your "7" key could be nothing on one char, and then only for the 7 key, it would send the input to the other selected app which is your hotkey for ranged attack on your ranger's box. This would allow you to spam auto attack on your ranger while in complete control of your other box, all while not breaking the following rule.
Third Party Programs
Any third-party programs that is designed to alter the client, sniff or alter the data communication between client and server, or automate any task within the client are expressively forbidden. Log parsers are OK.
In response to the original topic, these wouldn't automate shooting like many of ya'll were interested in. But it will, at the least, make it more convenient for you to play a ranger while boxing (which I'm assuming you are doing, b/c if you are asking for autoshoot for a single boxed ranger, then man.. you are fucking lazy).