[jQuery] Passing Values into internal variables

I'm using
http://www.learningjquery.com/2007/10/a-plugin-development-pattern to
develop my own plugin and I am stuck whilst trying to pass information
into the generated 'object'.
Something along the lines of setting the date on a calendar from
outside... such as you can do with the UI datepicker.
Is there a simple example of how to do this somewhere?
I've abstracted the code below as much as I can, the short story is
that plugin builds a list of items you can pick from and populates the
input with text when the item is selected.
Some code...
(function($) {
    $.fn.dc_thingy = function(options) {
        this.each(function() {
            var opts = $.extend({}, $.fn.dc_thingy.defaults, options);
            var $input = $(this);
            var selected = null;
            var timeout = null;
            // this is how I want the function to work !!!
            function setfromOutside(s){
                selected = s;
                build_thingy();
            }
            function setContent(text) {
                if (timeout) clearTimeout(timeout);
                $input.val(text).focus();
                $input.trigger('dc_select', [ text ] );
                $box.hide();
            };
            function buildThingy(date) {
                $box.empty();
                // make the contents
            }
            // no autocomplete
            $input.attr("autocomplete","off");
            // create a container div for the popup
            var $box = $("<div></div>"));
            // add it to the end of the body add a class, give it absolute
position and then hide it
            $box.appendTo("body")
            .addClass(opts.popupClass)
            .css("position", "absolute")
            .hide();
            buildThingy();
            // Add a class to the relevent input box
            $(this).addClass(opts.inputClass);
            // set the position of the box using the dimensions plugin and show
it if the input gets focus
            $(this).focus( function() {
                var pos = $(this).offset();
                $(".dc").hide();
                $box
                .css("top", pos.top + $(this).outerHeight() )
                .css("left",pos.left)
                .show();
            });
            // on mousedown reset position and reshow the box
            $(this).mousedown( function() {
                var pos = $(this).offset();
                $box
                .css("top", pos.top + $(this).outerHeight() )
                .css("left",pos.left)
                .show();
            });
            // hide the box when the input loses focus
            $(this).blur( function() {
                if (timeout) clearTimeout(timeout);
                timeout = setTimeout( function(){ $box.hide(); }, 300);
            });
            $(this).keypress( function(e) {
                switch (e.keyCode) {
                    case 13: // ENTER
                        if ($box.css("display") != "none") {
                            // select item
                            return false;
                        }
                        break;
                    case 27: // ESC
                        $input.focus();
                        $box.hide();
                        break;
                }
            })
        });
    };
    $.fn.dc_cal.defaults = {
        popupClass : 'dc',
        inputClass : 'dc_has',
    };
})(jQuery);