Try using ZIPPO lighter fluid. A little on a paper towel or rag will take off any sticky residue. Just remember this stuff is flammable. Just about any organic solvent will remove adhesive. Organic...
I would try steaming them.
>Answer.
Try using dishwasher liquid diluted in hot water. Score (make lines with a sharp knife just through the top layer) the paper, then thoroughly wet...
I use a product called "Goo-Gone". It's an oily orange substance that smells of petroleum. (I'm in the United States.) I've found that very non-polar solvents like oils (Goo-Gone, gasoline, mineral...