Why not just follow Biggs and Tank when they leave Tatooine and join The Academy. They meet up with a younger Porkins and Wedge and eventually join the Rebellion at the end, but Biggs makes a small stop on Tatooine to visit Luke before he meets up with the Rebellion at the end of the film. We all know this to be the Anchorhead deleted scene. You could clean up those scenes and add them to the new film.
Find actors who resemble a young Garrick Hagon, William Hootkins, and Denis Lawson.