Perhaps this could be done (indirectly) with the Windows accessibility options (MouseKeys)? I don't think the results would be great, though. Maybe a macro program of some kind? I've seen mentions of a program to use a gamepad/joystick as a mouse; maybe something like that would help.
Hotkeys can be modified, but I don't know if that can be done for mouse buttons/movement (
Tutorial-Changing F1-F12 hotkeys to different keys).
You can click on hold the left mouse button down to have your character move in the direction of the cursor, which can save on having to click repeatedly. Also, Ctrl-click will have your character target and attack the closest opponent to the cursor, reducing the need to move the mouse around.