Johnny Depp, Jude Law and Colin Farrell were concerned for two-year-old Matilda's future as Ledger only left an old will which did not include the child.
The three actors played versions of his character Tim in the fantasy epic The Imaginarium of Dr Parnassus after Ledger died in January.
Filming was suspended but director Terry Giliam opted to complete Ledger's role and finish the movie by using Depp, Law and Farrell to shoot his final scenes.
Giliam, 67, said: "They didn't take money - it goes to Heath's daughter.
"That's extraordinary. And wonderful and when you're part of that, you think, 'Ah, this is maybe why I went into the movies in the beginning. I thought it would be full of wonderful people.' And we've got a movie full of wonderful people who did extraordinary things to help."
The film is a modern day morality tale which tells the story of Dr Parnassus and his extraordinary 'Imaginarium', a travelling show where members of the audience get an opportunity to choose between light and joy or darkness and gloom.
The Brokeback Mountain star was found dead in his New York flat from an accidental overdose of prescription drugs.
Gilliam added: "It's the last chance to see Heath and he's brilliant."