Tipping isn't done until the last night anyway. And everyone has the option of having it added to their sail & sign card so not everyone gives an envelope to their waiter, room steward, etc. One thing you can do, is if you have extraordinary service, reward them at the end of the cruise with a little something extra. They all work very hard to take very good care of us and cater to us on our cruises.
Fortunately, I have not had any problems with any of the crew so far on 5 cruises. Hope it continues this way!