Bookmark this page in the mobile Safari browser of your iPad or iPhone and then follow this video tutorial to install the Site Search Bookmarklet.

"Site Search" Bookmarklet Source Code

javascript:(function(){void(q=prompt('What are you looking for?',''));if(q)location.href='http://www.google.com/search?q=site%3A'+document.domain.replace('www.','')+'%20'+escape(q)})()
iOS Bookmarklets →