Note: After saving, you have to bypass your browser's cache to see the changes. Internet Explorer: press Ctrl-F5, Mozilla: hold down Shift while clicking Reload (or press Ctrl-Shift-R), Opera/Konqueror: press F5, Safari: hold down Shift + Alt while clicking Reload, Chrome: hold down Shift while clicking Reload.
function addLink(where, url, name, id, title, key, after){
    //* where is the id of the toolbar where the button should be added;
    //   i.e. one of "p-cactions", "p-personal", "p-navigation", or "p-tb".
    //
    //* url is the URL which will be called when the button is clicked.
    //   javascript: urls can be used to do more complex things.
    //
    //* name is what will appear as the name of the button.
    //
    //* id is the id of the button; it's best to define one.  
    //   Use a prefix to make sure its unique. Optional.
    //
    //* title is the tooltip title that gives a longer description 
    //   of the button; if you define a accesskey, mention it here. Optional.
    //
    //* key is the char you want for the accesskey. Optional.
    //
    //* after is the id of the button you want to follow this one. Optional.
    //
    var na = document.createElement('a');
    na.href = url;
    na.appendChild(document.createTextNode(name));
    var li = document.createElement('li');
    if(id) li.id = id;
    li.appendChild(na);
    var tabs = document.getElementById(where).getElementsByTagName('div')[0].getElementsByTagName('ul')[0];
 
    if(after) 
{
        tabs.insertBefore(li,document.getElementById(after));
    } else {
        tabs.appendChild(li);
    }
/*
    if(id) {
        if(key && title) { ta[id] = [key, title]; }
        else if(key) { ta[id] = [key, '']; }
        else if(title) { ta[id] = ['', title];} 
    }
    // re-render the title and accesskeys from existing code in wikibits.js
    akeytt();*/
    return li;
}

function AddMyUploadLink()
{
addLink('p-participate', 'http://commons.wikimedia.org/w/index.php?title=Special:Upload&uploadformstyle=basic', 'Better Upload', 'temp-ul', 'Better Upload', 'n-uploadbtn');
}
 
$(AddMyUploadLink);