Memucan is not a minor courtier in Targum Sheni. He is Daniel under another name.
The targum explains that Daniel was called Memucan because heaven had arranged for Queen Vashti's death through him. He had already been exiled with the tribe of Judah, along with Hananiah, Mishael, and Azariah. Great and mighty works had been done through him, and now his court advice would turn the story toward Esther.
The Persian court has its own procedure. Younger ministers speak first, then elders correct them if needed. Memucan is the youngest, so he speaks first. The targum adds a personal motive: he has a Persian wife wealthier than himself, and he wants wives compelled to honor their husbands.
That mixture is characteristic of the Esther traditions. Human motives are small, tangled, and political. Heaven still uses them. Daniel speaks from inside the machinery of empire, and the result is the removal of Vashti, the opening through which Esther will enter. The court imagines it is managing household order. Providence is moving the throne.
Then said Memucan, who is Daniel. But why is he called Memucan? Because when the tribe of Judah were taken captive to Babylon, —Hananiah, Mishael, Azariah were among them,—Daniel also was exiled, through whom great, wonderful, and mighty works were done, and again through whom heaven determined that Queen Vashti should be killed, in consequence of which he was called Memucan, i.e. " establisher." And Memucan spake to the king and governors—there was a royal statute at the time which provided, that in the cabinet consultations the younger ministers should give their advice first. If it was a proper one, they carried it into execution; but if not, the older ministers gave their advice. And as Memucan was the youngest of them all, he gave his advice first. It so happened that Memucan had married a Persian wife who was richer than himself, and she refused to speak to him in any other language but her own, and so he thought to himself, now is the opportunity to compel the wives to honour their husbands. Therefore he said to the king and the nobles: "Not against the king alone has Queen Vashti failed, but also against all the nations and governors that are in the empire of Ahhashverosh.
