- in theory, yes... add a USB ethernet adapter to the n800, then use iptables to forward the packets through the wifi network interface... (you'll want to use some firewall rules as well)...

http://www.netfilter.org/projects/iptables/index.html

- you'll need a supported adapter, along with a port of iptables (netfilter), and a script...

here are a few script generators (just plug in your values and click a button, then copy and modify the resulting script):

http://easyfwgen.morizot.net/gen/
http://townx.org/simple_firewall_for...using_iptables