My first JS Hooks idea. Things got complex shortly after this :)

JS Hooks

/* bind to variable */

jQuery(document).ready(function() {
    // register a filter and override the functions
    jQuery('body').bind('myTrig', function(event, obj) {
        obj.valueOf=obj.toSource=obj.toString=function(){return "blue"};
    });

    // create a variable as an object and pass it to any filters that have been registered
    var o = Object('green');
    jQuery('body').trigger('myTrig', o);
    alert(o); // should return blue
});


/* bind to object */

jQuery(document).ready(function() {
    // register a filter
    jQuery('body').bind('myTrig', function(event, obj) {
        obj.value = "blue"; // set the value of the object instead of returning a value
    });

    // create an object and pass it to any filters that have been registered
    var o = {value: 'green'};
    jQuery('body').trigger('myTrig', o);
    alert(o); // should return blue
});