When I ask business speakers to try a more expressive style-to be louder, or to get their hands above their waist, I often hear them say, "That's not my style," or, "That's just not me."
Limiting your definition of self must be comforting, but sometimes as a speaker you need to act not as you would habitually, but as you must to achieve your goals.
In other words, you need to fake it 'til you make it. Actors rehearse until they discover and become the character. You can practice new behaviors until they become more natural.
You may have fixed traits, but to grow as a speaker, sign a free-trait agreement with yourself.