China Southern codeshare?
 

China Southern is part of Skyteam, but CO doesn't seem to make much use of them.

Would DCA-EWR-PVG-ICN and back (with China Southern doing the PVG-ICN-PVG legs) be bookable on Continental.com? It's a 1hr15min connection in PVG going and an overnight on the way back. I'd actually take a couple of days stopover in Shanghai on the return flight.

The routing is about 300mi longer than DCA-EWR-NRT-ICN, but shorter than a routing through LAX.

With that particular routing, you may have to book with the co.com support desk. If you are worried about EQMs you may be able to talk them into allowing you 100%EQM because it is not bookable online.

There is nothing to "talk them into" with the co.com desk. Book the first part of the trip (DCA-PVG) on co.com and choose pay with cash. Call the 800 number for co.com support, give them the PNR and have them add the PVG-ICN-PVG segments that you want. It'll reprice and then you can complete the transaction. And the whole thing is considered an online purchase. If you are buying something more than a WESTNL fare anyways just book it over the phone and save the hassle.