I actually did something like this last year with an overseas visitor. We just transited in XIY for 6 hours and took the bus down town to ride bikes on the whole length of the city walls. FWIW, this is what happened to us:

Even for a domestic connection in XIY CA in PVG would not transfer luggage explaining they do not offer this service in XIY. We tried to recheck our luggage after landing in XIY and they would not accept it until check-in started for the flight. That was not going to work for us since we absolutely could not take our bags so we used the left luggage service which was a set price per bag regardless of weight or size. This delayed our expected departure at least 30 minutes and added another 10 when we returned. I cannot remember exactly where the left luggage desk was but it was not close to the CA check in counter. Down on arrivals level, I believe.

If you have a trusted driver, I would leave your luggage in the trunk. I always take a picture of the car registration in full view of the driver so he sees what you are doing. My staff in China taught me this trick and I even do this with taxis if they are supposed to wait. Maybe you can carry your valuables on you. Do keep in mind though there are tons of people at the tombs so you need to be careful there.

It sounds like fun, hope you enjoy it!