gistfile1.js

    $$('a[data-remote=true]').each(function(a){
        a.onclick = function(){
            href = a.getAttribute('href');
            url = href.split('?')[0];
            params = href.split('?')[1];
            newParam = encodeURI(eval(a.getAttribute('data-with')));

            if(params){
                params = params.split('&');
                params.each(function(p){
                    if(p.match(new RegExp('^'+newParam.split('=')[0]+'='))){
                        oldParam = p;
                    };
                });
                params = params.without(oldParam);
            }else{
                params = [];
            };

            params.push(newParam);

            a.setAttribute('href', url + '?' + params.join('&'));
        };
    });