All things considered, it would be a lot easier for Stanley to film a confession, and then bury it in his archives for eventual discovery after his death, than plant hidden "clues" in his films.
If there are any intentional hidden messages in The Shining at all, it's akin to the Beatles doing backwards masking on purpose for a good laugh.
I knew a garage band in the early 90's that meticulously created a song that got really creepy when you played it backwards.