There a number of sites that advertise for share accomodation. You just need to google them. I can be harder to find short term because most people prefer longer term so that they don't have the room empty for time and they don't have the change in flat mates around the house. You will need to put up one month's rent and probably one month's security deposit but it is a case by case situation. I'd get a copy of the original lease and change accordingly. Make sure you get a reciept for all monies and also ensure it is very clear how the bills will be handled during your stay and when you leave. Put this into the contract so that you are both clear.

Adrienne
http://www.shanghaiprops.com