Oh great, matrix didn't show the option with the 15h connection on the date I selected, so I'll try another. That's definitely the way to do it - I don't want to count on a DPS agent agreeing to short-check.

And yes, I would have a Chinese 2-entry visa anyway for the $1323 CAN-PEK-LAX deal. So with these two tickets, I would use one entry to position to CAN, then I'll do a 144-hour TWOV at PEK on the way back from LAX by showing the TWOV desk the PEK-DPS ticket, which will leave me the second entry on the visa to show at check-in at DPS.