Reverse engineer the client code such that a little bot player runs around in game flipping levers and seeing if redstone torches are on/off. Then you would truly have a computer with a little guy running around inside it doing all the thinking.

The famous (is it?) minebot already implements about 99% of the required functionality and requires no server side mods. There are of course competitors to minebot some of which may be closer or further away from this goal.