Spoilers, yo.
Cutting everything that's trying to set up the Justice League, except Wonder Woman, we should now have time to make the following changes:
1) After the Senate explodes, Superman goes into action alongside first responders to help save people, or care for the bodies of the dead. He then appears in front of the news cameras and says:
"What I was going to say today...doesn't feel necessary now. Because what I know is this: I am only one person. I can be a beacon of hope but I cannot stop all the evil in the world, not alone.
But what I saw today was for every person in the Senate, five came running to help, then five more to tend to the wounded, and five more to the grieving, and five more to the dead.
So I know that we are in this together. That to represent the hope you need, all I have to do is look to my left, and my right."
(Intersperse cuts of Batman, Luthor, Wonder Woman and humanity at large)
2) Wonder Woman opens a telecommunications device: A woman, obviously royalty, appears.
"Mother. I am need of the tools of my office, again."
The queen smiles. "I am pleased to hear you are taking up your mission again, Diana."
(Through the next bit, cut in scenes of Diana opening the containers that hold her tools of office and gearing up)
3) Superman confronts Batman. Batman hits him with the kryptonite grenade, they fight on the rooftop until Batman finally drops Superman into a building.
"Stop!" Batman says and Superman freezes mid punch.
"We don't have much time! Luthor's manipulating us both."
"Then why did you shoot me?"
"I had to get us to a place to talk where he couldn't see. I'm sorry. I was wrong about you, I didnt' see it until it was too late. We have to hurry. Luthor's planning something with Kryptonian technology and I don't think I can stop it alone," Batman says.
"He has Martha."
"Who?"
"My mother."
Batman's fists clench so tightly you can see the white knuckles beneath the armor.
"Where?"
"He'll kill her if I don't bring him your head."
"Nobody dies tonight. You stop Luthor. I'll save your mother."
Superman looks doubtful, Batman holds out his hand.
"Trust me."
They shake.
"OK, here's what you do next-"
Building implodes, and we go to the Doomsday sequence.