Well.... besides the 2 hour MSP connection, and the seats available to sell on galileo....

My bet is if there's a delay in DFW, you can ask to be rerouted DFW-MEM-LAX leaving DFW 7:36pm to arrive LAX 11:39pm-- note, though, that the DFW-MEM is very very full, also-- but the DFW gate agent is the one who would have authority to confirm you on it. MEM-LAX looks fine. True, this puts you into LAX an hour after the ONT flight, and NW will cover the SuperShuttle if the delay was due to a mechanical delay or oversell, but most likely you'd be rerouted via these NW flights.

In the event you run into trouble in MSP, there's a 9:10pm LAX flight-- granted, this is showing pretty full, and it's only 6 min. later than your ONT flight, but it's an option.

If you're a very good sweet-talker, you can ask for the 5pm connection via IAH on CO to arrive 9:50pm, but my hunch is that only under extreme circumstances will the agent route you onto CO.

Good luck!!