The lubricant is applied to polyurethane parts just to limit noise when they are moving against a steel component, where you have the polyurethane moving on a steel part like on a sway bar bushing. If there is no motion, movement/rubbing between the polyurethane and a steel component, you do not need to use any lubricant. I don't think that there is any real movement between the top of the spring and the shock tower, so you really should not need any lubricant there. You can put some lubricant on one or both sides if you like, it will not hurt anything, but it should not be necessary.
