For latex, and some oil based paints, you can use a steamer. You may need to remove the pan on the steamer but it is very effective. Once the paint has softened, use sharp pointed tools to gouge out the paint. Be very careful not to damage the plaster while doing this.
If this technique does not work for your paint, use a chemical stripper. Peel away is ok, but expensive. If you want to use a chemical stripper, other then PeelAway, be sure to also buy a thickener for it. I use Cab-O-Sil from Cabot Corp out of Boston. You want the stripper to be thick so it will stay on the cornice. Also, some chemical strippers may be required to be neautralized before you can paint, you need to find out if PeelAway requires this also. Once the stripper has been applied cover it with polyethylene sheeting so it will work longer without drying out. Try the chemical on some of the poly to be sure it wont eat it. If it does then try a different type of poly or a different stripper.
Keep experimenting with different tools to scrape into the details and dig out the paint.