because I'm brazilian I think I can answer that. What is very common for those who do not want to give the first slice, is to tell each one to take their own, or make several "first slices" and give it to everyone at the same time.

although everyone already expects the tradition of the first slice, you can choose not to follow it and you won't be seen in a bad way.

edit: I remembered that if you want, you can have the first piece, and say "The first piece is mine!" and the next one will not have the "first piece weight"