well I think how you do it is by pulling a bit of story that is implied and spoken of in the books and actually show it. Some type of meeting of the Landsraad where Leto scores big- making the emperor take note, followed by him telling his mentat that he wants a super secret meeting with the Baron, perhaps overheard by a Bene Gesserit that then in turn makes plans to visit Paul, and talks about the breeding program being in jeopardy if Jessica dies and hasn't produced a girl to wed to the Harkonnens. Something like that (done way better than my explanation obviously) to give the audience a clue... Basically a bit of story just before the book starts, to show who the players are, before we get to totally screwing the Atreides.
Jedi Dade