Was too lazy to read through this whole thread, but my n800 works fine in wlan ad-hoc mode while being connected to internet via bluetooth/mobile phone. All I needed was the missing iptables module which i was able to build against the installed kernel and some iptables user space libraries to get the nat working. With that setup I can provide several people with network (slow but existing) anywhere while they connect to the n800 in ad-hoc mode. I would expect this to also work without much problems, when I got time I'll give it a shot.