We travelled on Diamond Princess to Hawaii October 07. We just visited the pursers desk and had the tips removed . As we had booked anytime dining we felt that we would preferto tip who we got the service off as drinks etc are loaded by 15% anyway - there was no problem in doing thi.
This subject has been raised recently on 4 January and there are quite comprehensive answers which you might like to look at!! Around page 6 at the moment.
Perhaps it would be worthwhile typing in to the KEYWORD section individually......"£10.50", "tips" and "gratuities" and you should get a plethera of information ....Nei.