Handshakes, but that's a bit impractical even with the stooping, so Shepard doesn't offer. She does straighten back up to a more formal posture, less for the extra few centimeters than the courtesy factor. Man, this must be what volus feel like constantly.

"Shepard. Sentinel if you're looking me up on the team roster." No relation to a certain crappy Prime, probably. "Welcome aboard, Drift."

Drift would have to be an unusually suspicious soul to doubt that he is indeed welcome, because Shepard firmly believes it, and also firmly believes her word is law even if she doesn't quite realize that what she believes. Technically she's not in command here, sure, but once learned, the habit of authority never entirely goes away.