I don't know anything about the west coast, but, I've been known to do this on US bouncing around the east coast. The trick is simply on ITA to tell it to force connections on your itinerary on a certain airline. e.g.

SMF :: UA UA UA+
COS :: UA UA UA+

That's SMF to COS on 2 or more UA segments. You can also force a connection somewhere (e.g. X:LNK for a stop in Nebraska)