Here is version Stephen Wolf did at DKE:
Congress should provide that DC voters vote in Maryland federal electors, and until after the 2020 Census give Maryland+DC 9 representatives for a total of 436. The Maryland legislature would do the redistricting with a requirement that DC be wholly within one congressional district.
The 3 presidential electors for DC would not be appointed, or perhaps might be appointed by the two Houses of Congress and the President. Maryland+DC would have 11 presidential electors.
Each Maryland district would need to give up about 13,000 persons.
In the above map MD-2 and MD-7 could retract a bit towards Baltimore, which would produce a net change of 52,000 for MD-6 to MD-3 pulling, MD-3 further north between Baltimore and Washington.
The shifts could continue through MD-5, MD-4, and MD-8, with the addition to MD/DC-9 being on the northwest side of the district into Montgomery.
This would made MD-5 a bit more exurban, and bump the black share of MD-4 up, and put more of Montgomery in SB-8.
Given that Congress has time, place, manner regulation over congressional elections, it could impose the congressional boundaries - since Maryland is unlikely to act rationally.
So the Democrats get another voting representative at the cost of two electoral votes, and the voters in the district get to vote for representatives and senators, and Maryland gets better congressional districts. It is a Win-Win-Win-Win deal. Trump will be proud.