almost impossible by all i know about snakes. you would need to have very slim shoulders and another big problem would be to make the snake swallow you alive without constriction. there are ways to manage that but there ever will be a risk it wont work and the snake will start to constrict you. also you would need to have air supply and used air disposal cause it would last a very long time until the snake have swallowed you. and do not forget about the many long razor sharp teeth that will perforate your body by every single move of the snakes jaws again. once you will have reach a wider deep inside the snake the stomach acids will massive harm you. and at least you will have to need one or better more persons that make the snake regurate you whats possible in many ways but theres still a risk the snake wont regurate you. all in all not that easy as it may looks to an spectator.