Is there a method I can override on a JavaScript object to control what is displayed by console.log?

There's no way I know of. Your best bet will be to define a toString() method on the object you want to log and then call it, either directly or indirectly:

var o = {};
o.toString = function() {
    return "Three blind mice";
};

console.log("" + o);
console.log(o.toString());