The 23rd Amendment says (paraphrasing) that the District of Columbia has three electoral votes (exact wording will be at the end). Even if the rest of DC were granted statehood, the federal district would still have these votes.
My idea is to make the federal district not hold elections of its own, because it only holds things like the White House and the Capitol Building. (This is actually how the DC statehood bill is planned to be passed.) But, to satisfy the 23rd Amendment, the federal district would give its electoral votes to whoever wins the most votes in Douglass Commonwealth, or whatever it is called. The President already does not vote in DC (Trump voted in Florida, Obama voted in Chicago, etc.), so I don’t see how that would disenfranchise actual voters.
It requires a minimum of ⅔ votes in order to pass a constitutional amendment. In other words, ignoring the filibuster, could carbon-copying the electoral votes be done with a simple majority, like adding a state to the Union? (I understand this move could be seen as partisan because it effectively gives Democrats 3 more electoral votes. But repealing an amendment requires a supermajority of votes.
Exact wording of the 23rd amendment, since that might be relevant:
Section 1. The District constituting the seat of government of the United States shall appoint in such manner as the Congress may direct: A number of electors of President and Vice President equal to the whole number of Senators and Representatives in Congress to which the District would be entitled if it were a state, but in no event more than the least populous state; they shall be in addition to those appointed by the states, but they shall be considered, for the purposes of the election of President and Vice President, to be electors appointed by a state; and they shall meet in the District and perform such duties as provided by the twelfth article of amendment.
Section 2. The Congress shall have power to enforce this article by appropriate legislation.