We found it easy to just put the tips on the onboard account. You do have to go to Guest Services to do this, but it only took about 5 minutes. They just printed out a little receipt that you then put in the envelopes they provided. Each receipt was personalized to server etc.
Since we had Palo's reservations on the last evening we weren't sure if we would make to to the dining room to present the tips to the waiters. This way we were sure they would get them!