You’re on the right track 🙂
See section entitled “And what if the program I need is not available in the existing packages?” on that very page you linked to.
Obviously you need to execute these commands on a linux box with internet access. It then automagically downloads and installs a lot of stuff so that YOU can compile packages (ipkg’s) for YOUR specific device.
So, thats what you want, isn’t it? 😉