I not sure you can , chemical strippers will be an easy option but will be absorbed into the plaster . I assume this is a large ornate moulding that has lost some of its detail by heavy emulsions ? try a steam stripper and carfully scrapping away with a piece of softwood .
Thanks for that. Yes, a steamer did help - it still didn't come away in those big, satisfying chunks like wallpaper does, but it certainly softened the paint it and reduced the risk of chipping the plasterwork.