I use PaintShop Pro and am trying Eye Candy at the moment, I have added the files in the already installed Eye Candy 4000 Folder to a self extracting archive using winrar, then, uninstalled Eye Candy and deleted all registry entries, extracted the setup file with the /s switch and edited a picture in PaintShop Pro, everything seems ok but haven't tested it on a virgin system so there may be a problem I cant see.
You can still uninstall it with the unwise.exe, but may need to scan the registry for references to add it to ADD\Remove, or go
Here and try some of the switches listed.