Tal como acontece com todas as questões possíveis relativas aos regulamentos de Passaporte e Visto dos EUA, isto é amplamente abordado no Manual de Relações Exteriores.
Em primeiro lugar, depende de quantos anos esse viajante é, e com quem eles estão viajando. Por exemplo,
7 FAM 085 PASSAPORTES E VISTOS DOS EUA E DUAL NATIONALITY declaram:
a. Section 215(b) of the INA (8 U.S.C. 1185(b) and 22 CFR 53 require
U.S. citizens to enter and depart the United States on U.S. passports,
with limited exceptions.
d. See 9 FAM 40.2 Notes, 9 FAM 42.12 N4 (2)(b) and 9 FAM 42.71 N5.
Quais são essas "exceções limitadas", você pode perguntar? 9 FAM 202.1-2 você cobriu.
Applications for Visas for Certain Dual National Children:
(1) You should advise parents who apply for visas for dual national
children that regulations prohibit the issuance of a visa or other
documentation to a U.S. citizen or national for entry into the United
States as an alien. The children of foreign government officials,
however, may use their foreign passport for entry into the United
States.
(2) After the U.S. citizenship of a child has been determined by a
citizenship officer, the consular officer may, to avoid delay or
difficulty, give a written statement to the parents for presentation
to carriers or immigration officials. The statement should make clear
that the bearer of the foreign passport is a dual national child of a
foreign government official or employee who is traveling to the United
States on official business and as such may enter the United States on
the foreign passport as an exception to the provisions of INA 215(b)
regarding valid passport requirement.
(3) A child under 12 years of age who is included in the passport of
an alien parent in an official capacity may be admitted if evidence of
U.S. citizenship is presented at the time of entry. A determination of
the child’s citizenship should be made by citizenship officer prior to
departure from a foreign country and the parent should be instructed
to have evidence of such citizenship available for inspection by the
admitting Department of Homeland Security Officer.
Então, se seu amigo estiver viajando com os pais dele, e eles forem representantes em uma designação oficial, ele poderá pedir a um funcionário consular uma carta declarando isso.
Se, no entanto, ele só quiser evitar ser identificado como cidadão dos EUA quando sair do país, estará sem sorte. É ilegal emitir vistos dos EUA para cidadãos dos EUA.