I believe the proof for the conjectured statement was proven in the affirmative in the paper "Fields of Surreal Numbers and Exponentiation" by Dries and Ehrlich. Specifically, Lemma 3.3 on page 6 : http://www.ohio.edu/people/ehrlich/EhrlichvandenDries.pdf
If this satisfies the conjecture adequately great, if not, let me know if you would like to work toward a solution together on something similar or related.
Proof Already Exists?
I believe the proof for the conjectured statement was proven in the affirmative in the paper "Fields of Surreal Numbers and Exponentiation" by Dries and Ehrlich. Specifically, Lemma 3.3 on page 6 : http://www.ohio.edu/people/ehrlich/EhrlichvandenDries.pdf
If this satisfies the conjecture adequately great, if not, let me know if you would like to work toward a solution together on something similar or related.
Thanks.
-Vincent Russo