How do i add a query string pair to an existing url in jquery

Question

I am aware that I can access all external links on a page using something like:

// Get external links
$.expr[':'].external = function(obj){
return !obj.href.match(/^mailto\:/)
        && (obj.hostname != location.hostname);
};

does anyone know how I can add a query string pair (along the lines of ?aid=1234567) to the URLs in the external links?

Thanks in advance