Here is a quick and easy way to add this to the "Toolbox" at the end of the sidebar. Add this code to the end of MultiUpload.php:
// Hook to toolbox:
$wgHooks['BaseTemplateToolbox'][] = 'onBaseTemplateToolbox';
function onBaseTemplateToolbox( $sk, &$toolbox) {
$toolbox['multiupload']['href'] = Skin::makeSpecialUrl('MultiUpload');
$toolbox['multiupload']['msg'] = 'multipleupload-toolbox';
$toolbox['multiupload']['id'] = 't-multiupload';
return true;
}