Can I stay in China for more than 3 mos if I can get guarantee from China National?thanks

Hi....hello....I applied for double entry visa last time and it will end this Dec 2011, I did used it one time last july...now because of business matters I need to stay for about 3 months...will it be possible for me to get a new visa to enter China that will allow me to stay as I needed....or can I reapply the visa and extend my stay once I arrived in China ? (i understand I can only stay for a month as clearly stated on the paper), rather than going back and forth for 3 times...through HK...from Shanghai....please I need some insights...thanks... will it be beneficial for me if there is a China National who can give me an invitation letter and letter of guarantee, will that help me to get the visa for longer stay in China? Tried many times to call the China Embassy...but the lines were so busy.. ...please I really need more info on this matter....thanks again.....