I was able to easily share a wireless connection on my tablet by using a small proxy server:

http://www.acme.com/software/micro_proxy/

(attribution style license, very compact)

Yes, I could turn it into a full NAT router using iptables or such, but I just needed to update some wireless drivers for my laptop so I needed to use my tablet to connect to the internet wirelessly, but ethernet to the laptop until the new drivers were installed.