Can I leave china and return to pick for one night before flying home?

Basically I am in China on a single-entry 2 month business visa- I have booked my flight back to the UK but the week before I would like to do a round trip from my present location in Shanghai to Hong Kong, then on to Tokyo, then Seoul and finally return back to Shanghai ideally the day before my flight home...so i can pick up my bags and prepare for my return flight home...Is this possible? would it be possible to attain a 72 hour free transit for this purpose as essentially I'll only be returning to shanghai to pick up my bags and stay the night before catching my flight the next day....I would appreciate any advice
Thanks