I have to say this - I was on Delta Queen and I partially pre-tipped the room steward for my Mom because I knew she was going to need some things - like water, etc.
It did me absolutely no good at all. In fact it was some of the worst service I had ever had. I think he may have thought that was the only tip I was going to give him for the whole cruise. So, if you do this, be sure to explain what you are doing. "this is a bonus to get us started, this is not your entire tip."
See, in my case I was so mad I may not have given him any more money - and then (being not used to our culture) I now realize this exact scenario may have happened to him before. So he came to believe that people who tip a small amount at first don't plan to tip any more.
The alternative would be to give them the whole tip first, including any extra - then they KNOW what your intentions are, but you still have no guarantee they aren't just flakes - so that is risky.