The West Wing Episode Guide has more information on the writers and directors of the upcoming episodes:
""Election Day Part II"
Written by: Eli Attie & John Wells
Directed by: Christopher Misiano
Written by: Eli Attie & Debora Cahn & John Wells
Directed by: Steve Shill
Written by: Peter Noah
Directed by: Nelson McCormick
"The Last Hurrah"
Written by: Lawrence O'Donnell, Jr.
Directed by: Tim Matheson (also plays former Vice-President John Hoynes)
Written by: Debora Cahn
Directed by: Lesli Linka Glatter""
Gordon Shumway posted at Television Without Pity:
"[Episode 21] is Debora Cahn, and the finalé is John Wells."
kendrakp posted at Television Without Pity:
"The final episode titles:
Election Day II
The Last Hurrah
Tomorrow (series finale)"
And a poster at WWSpoilers added all the writers for the upcoming episodes:
"Election Day: Lauren Schmidt
Election Day II: Attie, Wells
Requiem: Wells, Cahn and Attie
The Last Hurrah: O'Donnell
Institutional Memory: Cahn