This is just my method which I figured out after LOTS of headaches.
I usually lay paper towels over that stuck like #%*$! platen paper, and then dribble mineral spirits (paint thinner) over the paper towels. The paper towels are just there to hold the thinner, and help keep it from drying out.
It soaks up both the platen paper and the adhesive. The whole thing will scrape off the next morning quite easily. Kerosene works too, maybe better, but is prolly more stanky.
After soaking overnight or several hours, I scrape the mess off with the same smoothed metal putty knife (with rounded corners) I use to scrape ink off of my screens. Then the remaining adhesive is a thick jelly-like substance which IS A PAIN to remove, but I currently use Lacquer Thinner or Goof Off to remove that until I can find something that works better.
My platen paper is either R-Tape or Transfer Rite, and the bulk of my adhesive is that liquid that smells like Elmer's Glue.
Not too bad, but messy. Hope that helps!