Don’t know if this has been suggested yet, but how about having Palpatine’s Fortnite broadcast either replace or preface Starkiller Base firing in Force Awakens? Find or create additional footage for a montage of people hearing it across the galaxy, throw in the Resistance guy’s TROS line speculating as to how he’s alive.
Introduce that right away in the trilogy, then (as has already been suggested) move Kylo tracking Palps down to somewhere in Last Jedi, along with whatever other lines can be altered or added to integrate his survival into the trilogy.