@birgitt: Instead of a labor intensive process of spraying and paper or cloth, could you not include the lubricant in a separate reservoir and apply a bit with each flush, avoiding the need for a manual process? Or perhaps have an automatic cycle where the bowl drains, the lubricant is applied, and then water is supplied to refill the bowl after a period of time has elapsed (if necessary)?

It seems manual application is likely to slow adoption IMHO. If automated, seems like a slam dunk for heavy use/commercial/public applications though.