"Padme would still work; are you suggesting Luke never learned the name of his mother? By that logic Luke never learned the name of his father until Obi-Wan said "Anakin was a good friend" in RotJ. "
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Are you suggesting that Luke knew he was the daughter of the queen of Naboo? No, clearly Luke does NOT know his mother's name anymore than Leia knows her father's name is Anakin Skywalker.
At least that's the best interpretation of what's actually there. For Vader to be able to use "Padme" in a sentence with Luke and expect him to know who "Padme" is, we should see someone tell Luke.
It all seems so much simpler and story enhancing to have Obi Wan reach out to Anakin in ANH during the Duel. It might go better somewhere during the beginning of the duel -- as Obi Wan first sees Vader: "Anakin..." He says in his Jedi mind voice. "That name no longer holds any meaning for me." replies Vader. Bzzaammmm... Obi Wan lights up his Saber and starts talking to "Darth".