I did this once. I wanted a table for two and was on a 7 day cruise. I think it was a Holland America cruise. Here is what I did. As soon as I got on board I went to the dining room and offered the maitre d' a twenty dollar bill. He refused it and told me that it wasn't necessary serving my desires was his job.
I took the table and then tipped him at the end of the cruise.
BTW, we hated the table for 2. Decide we would never do that again.