Firstly Han should miss the Sarlacc’s tentacle, instead Luke hits it via deflecting a blaster bolt.
Then make some changes to the briefing room scene, so that Han is supposed to lead the fighter attack and Leia leads the ground forces. I have no idea how to do that yet, maybe redub General Madine.
And then we nee a scene where Han talks to Lando and tells him to lead the fighter squadron in his stead. Two scenes might work as a template, the hangar scene where Han tells Lando to take the falcon or their short conversation before the briefing begins. The only really difficulty should be the dialogue.
And while I’m at it here is another idea. Maybe have Han offer to help doing repairs to the falcon and Lando declines explaining that no repairs are necessary. Just a little notch adding to Han’s feeling of uselessness as in his absence the falcon has finally been fully repaired.
Anyways as you can see I am really just brainstorming over here.