Air_King
§ 61.75 Private pilot certificate issued on the basis of a foreign pilot license.
(a) General. A person who holds a foreign pilot license at the private pilot level or higher that was issued by a contracting State to the Convention on International Civil Aviation may apply for and be issued a U.S. private pilot certificate with the appropriate ratings if the foreign pilot license meets the requirements of this section.
(b) Certificate issued. A U.S. private pilot certificate issued under this section must specify the person's foreign license number and country of issuance. A person who holds a foreign pilot license issued by a contracting State to the Convention on International Civil Aviation may be issued a U.S. private pilot certificate based on the foreign pilot license without any further showing of proficiency, provided the applicant:
(1) Meets the requirements of this section;
(2) Holds a foreign pilot license, at the private pilot license level or higher, that does not contain a limitation stating that the applicant has not met all of the standards of ICAO for that license;
(3) Does not hold a U.S. pilot certificate other than a U.S. student pilot certificate;
(4) Holds a medical certificate issued under part 67 of this chapter or a medical license issued by the country that issued the person's foreign pilot license; and
(5) Is able to read, speak, write, and understand the English language. If the applicant is unable to meet one of these requirements due to medical reasons, then the Administrator may place such operating limitations on that applicant's pilot certificate as are necessary for the safe operation of the aircraft.
As far as the regulations are concerned, I don't think you need to see a designated examiner for what you're trying to accomplish.
You might want to look into visiting the FAA office in Singapore. As long as your paperwork is all in order, and you meet the requirements listed above, they may be able to help you out. If Singapore doesn't work, you are probably going to have to visit a FSDO office to accomplish what you're trying to do.
Designated examiners are for examinations, not for issuance of a pilot certificate based on a foreign one!