It seems doable (for someone who is not me, anyway) to replaces the Snokes in a jar with Palpatines. It would essentially just be a still image mapped over and tracked for the shot.
I don’t know if this has been discussed yet, but apparently in the novel Palps “spirit/force ghost/whatever” is in a clone that degrades since the clone cannot house him … literally falling apart to do so. Kinda what I was expecting the direction they were going.
I like the idea of putting some Palpy bodies in those tubs to “help” answer the question why/how Palps is around … I don’t like comics/books/tweets/etc. that explain things in a movie OUTSIDE of the actual movie. We don’t ned EVERYTHING be overly explained, but for major plot points … we need some kind of answer or at least applied reasoning.
By doing what you are proposing HAL, it would help answer the question without being overly blatant and over explaining things.