It can't be Flynn or Rogers. It has to be someone who has already been through the Senate approval process for an authoritative political position. Any authoritative position, so long as it was approved by the nominating/approval process. Flynn was in a position and Rogers resigned and would have to go through it again. He could, however, reposition someone from another department, someone else appointed in the DOJ, etc.
See 5 USC 3345(a)(3)
or (3) notwithstanding paragraph (1), the President (and only the President) may direct an officer or employee of such Executive agency to perform the functions and duties of the vacant office temporarily in an acting capacity, subject to the time limitations of section 3346, if--
If the position does not absolutely require legal training, how about....Zinke?
Retired SEAL (In fact, commanded SEAL Team 6 IIRC), took all of 60 days to square Interior away and....
Geesh, I've met and talked with the man a half dozen times and he would hit DOJ like a neutron bomb in the Fulda Gap.
...the heads would be 'sploding all over the Beltway.