There is no how-to. You would have to do it on your own. But most of them are in /var/opt/rcware /tftpboot/ and you will also need /www/ and of course the init scripts /etc/init.d/ - scripts and nginx and maybe some libraries…
By the way what is the purpose of this? We worked hard on making the system as much read-only as possible in order to keep your sd card safe... It might be easier to install your packages on the distribution that we created.