Non so se possa aiutare, io per passare un'intero link ho sfruttato l'attributo alt ed ho modificato queste parti ( sto parlando di jquery.lightbox-0.5.js ) :

Codice PHP:

            
if ( jQueryMatchedObj.length == ) {
//                settings.imageArray.push(new Array(objClicked.getAttribute('href'),objClicked.getAttribute('title')));
                
settings.imageArray.push(new Array(objClicked.getAttribute('href'),objClicked.getAttribute('title'),objClicked.getAttribute('alt')));
            } else {
                
// Add an Array (as many as we have), with href and title atributes, inside the Array that storage the images references        
                
for ( var 0jQueryMatchedObj.lengthi++ ) {
//                    settings.imageArray.push(new Array(jQueryMatchedObj[i].getAttribute('href'),jQueryMatchedObj[i].getAttribute('title')));
                    
settings.imageArray.push(new Array(jQueryMatchedObj[i].getAttribute('href'),jQueryMatchedObj[i].getAttribute('title'),jQueryMatchedObj[i].getAttribute('alt')));
                }
            }

...
...
...


/*
            if ( settings.imageArray[settings.activeImage][1] ) {
                $('#lightbox-image-details-caption').html(settings.imageArray[settings.activeImage][1]).show();
            }
*/
            
if ( settings.imageArray[settings.activeImage][1] ) {
                
lnk "" lnk1 "";
                if ( 
settings.imageArray[settings.activeImage][2] ) {
                    
lnk '<a href="' settings.imageArray[settings.activeImage][2] + '">';
                    
lnk1 '</a>';
                }    
                $(
'#lightbox-image-details-caption').htmllnk settings.imageArray[settings.activeImage][1] + lnk1 ).show();
            } 
se c'azzecca qualcosa adattalo pure alle tue esigenze