Here's what I would have done if I could excise the Byron arc and replace it with the Telepath War:
Season 4
4X1 Hour of the Wolf
Whatever Happened?
Summoning
Falling Towards Apotheosis
Long Night
Into the Fire Part One
Into the Fire Part Two
Epiphanies
Illusion of Truth
Atonement
4x11 Racing Mars
Lines of Communication
Conflicts of Interest
In Valen’s Name (Babylon 4 & Valen)
Rumors Bargains Lies
Minbari Civil War Battle
Moments of Transition
No Surrender No Retreat
Additional Earth Civil War episode
Exercise of Vital Powers
Face of the Enemy
4x22 Intersections in Real Time
Season 5
5x1 Between Darkness & Light 1
Between Darkness & Light 2
Endgame 1
Endgame 2
Rising Star
The Deconstruction of Falling Stars
No Compromises
The Day of the Dead
Telepath War 1
Telepath War 2
5x11 Telepath War 3
Telepath War 4
Telepath War 5
Ragged Edge
Meditations on the Abyss
Darkness Ascending
All My Dreams Torn Asunder
Movements of Fire and Shadow
Fall of Centauri Prime
Wheel of Fire / Objects in Motion (a lot of the Lyta stuff would be cut / changed around if the Telepath War has already happened)
Objects at Rest
5x22 Sleeping in Light
Of course, a lot of subplots would have to have been changed around if the Telepath War to take place within the 5 year arc of the series, rather than several years later. But I think this would have been an interesting way to go. As you can see, the Earth Civil War arc is the main thing that I think should be stretched out a bit if one is allowed to extend it into Season 5.
Also, going against the grain of popular opinion here, I really love "Deconstruction", so I would want to keep it, even if it doesn't work quite as well if it isn't a season finale. And I would keep Garibaldi on Mars for a while after "Rising Star", into at least the early part of the Telepath War.
(Incidentally, early JMS notes on Season 5 apparently had Garibaldi staying on Mars for much of the season, but still being a featured character on the show. I'm wondering if the change was made for budget reasons. Too expensive to spread your cast around to too many different settings, and have them interact with too many guest stars.)