I cannot drink alcohol and practice the piano afterwards, that is for sure. Even a very small amount ruins my fine motorics. So I guess it would be even worse to do it in connection to performance.
In order to get more emotional you must work with yourself at home when you practice. Your practice room is your private workshop and laboratory, you are entitled to do whatever you like there. Sing and dance and be silly - nobody is watching! It is not just your hands that are supposed to "feel" the music and play the music - it is your whole body. I recommend that you take a class in Dalcroze eurythmics. I also recommend that you read a book like "The Perfect Wrong Note" by William Westney.
I am not suggesting that you must turn your performance to freakshows, mind you. But you know that actors do a lot of physical exercises during their training. They scream, make faces, roll on the floor, in order to learn to use their bodies and voices. And that will qualify them to whisper "to be, or not to be" later on.
Far too many pianists today take themselves too seriously. If you perform, how to you introduce yourself? Do you just bow and sit down to play? Or do you talk to the audience, present the piece and the composer, telling a few little interesting facts, maybe describe what you think the music will say, if there are any radical ideas etcetera? You don't have to talk for hours but if you take two minutes, where you smile at your audience and they smile back at you, you will create a much more forgiving, relaxed atmosphere. They realize that you are human, that you have worked hard with this, and you realize that they are not hostile. So, it may be different if you are in a competition, I suppose you are not even allowed to talk there - but being in a competition is not mandatory and besides I think this whole competition concept STINKS. Music is about art, joy, love!