I've never had silicone that wouldn't cure, eventually. Moisture is what causes silicone to cure and there is normally plenty of moisture in the air. I've used mineral spirits to thin pure silicone caulk and then used it to glue tieout loops to silnylon. These always cured within a few days. When I do this, I have always tried to use fresh silicone. Google suggests using alcohol to remove uncured silicone, either Isopropyl or denatured Ethanol. Mineral spirits might work. I've never used alcohol to thin silicone. There is water in most alcohol and I would expect that water to help cure the silicone. I wouldn't suggest a strong solvent like Lacquer thinner or Acetone, partly because of the fumes and partly because they might do more damage than good. Even alcohol needs good ventilation and rubber gloves. I would suggest trying some of these solvents on a small spot and see whether they do anything. Ordinary paper towels may be too flimsy, you might need paper shop towels to wipe the residue off.