Thanks a lot to both of you for taking the time to reply. I didn't know that you could fly on a "N-" aircraft with a foreign licence provided you're flying in a country (not U.S.) where the licence is valid.
After reading your comments I also read a few pages of the new regulations for fractional ownership programs (issued Sept. 2003), and found some interesting information...
§ 91.1053 Crewmember experience.
(a) No program manager or owner may use any person, nor may any person serve, as a pilot in command or second in command of a program aircraft, or as a flight attendant on a program aircraft, in program operations under this subpart unless that person has met the applicable requirements of part 61 of this chapter and has the following experience and ratings:
(1) Total flight time for all pilots:
(i) Pilot in command—A minimum of 1,500 hours.
(ii) Second in command—A minimum of 500 hours.
(2) For multi-engine turbine-powered fixed-wing and powered-lift aircraft, the following FAA certification and ratings requirements:
(i) Pilot in command—Airline transport pilot and applicable type ratings.
(ii) Second in command—Commercial pilot and instrument ratings.
(...)
(b) The Administrator may authorize deviations from paragraph (a)(1) of this section if the Flight Standards District Office that issued the program manager’s management specifications finds that the crewmember has comparable experience, and can effectively perform the functions associated with the position in accordance with the requirements of this chapter. Grants of deviation under this paragraph may be granted after consideration of the size and scope of the operation, the qualifications of the intended personnel and the circumstances set forth in § 91.1055(b)(1) through (3). The Administrator may, at any time, terminate any grant of deviation authority issued under this paragraph.
If your interpretation is similar to mine, this means the guy we're talking about has nothing to do as SIC in the aircraft, since he doesn't have an FAA licence/rating and has less than 500 hours.
And, of course, here the concept of "safety pilot" is absolutely nowhere to be found. Case closed, I would say...