I think the best idea to retroactively tie the sequel trilogy films together is by doing it the subtle way. For example, the brief Palpatine hints that are scattered across the Rekindled edit of TLJ (like his silhouette at the cave scene, his laugh during Luke’s flashback, or Snoke’s eyes turning yellow after he’s mortally wounded), that culminate in Palps’ “find me” at the end.
For example, the vision in TFA would be a great part to put a hint of Palpatine’s involvement, like the shot where young Rey watches Ochi’s ship depart Jakku.