But DD had flashbacks to his own origin. The FF could have that, so that it doesn't start off the movie (or whatever movie they're in) in a linear way but just jumps straight into the action, and then they can recount the origin later if someone asks about it. Or they could have a slideshow-style presentation a la Iron Man when Tony Stark was first being introduced in the first movie (after the Afghanistan capture scene, of course).
They could even have something similar to the Smithsonian Museum presentation of Cap in Winter Soldier with someone narrating in the background, as if it is a well-known event that is now celebrated.
What would be cool is if Johnny Storm met Cap and was slightly starstruck, and Cap could tell Johnny that he was like him once, as a nod to Evans having play Johnny as well. Of course, I don't know how realistically this could happen, given that Cap is on the run.