One additional thing I've noticed - in the new DL.com (within My Profile, in the Basic Info box), there is a place to include/edit your twitter handle.

Though I never actively provided this through DL.com, it does have my correct twitter account, so I think that @DLAssist puts a note in your Skymiles profile after they identify who you are. And I suppose you could help them out by just adding it in yourself on DL.com.

I tested this a couple weeks ago (by accident, actually, just forgot to put in the PNR like I usually do) when the DL app wouldn't let me pick an EC seat for some reason. Just DM'd something like "Trying to get seat 10C on AAA-BBB tomorrow but phone app won't save it." They came right back and said they'd assigned the seat, and my seat map immediately showed the correction when I went back and checked.