US expat exercising options under Regulation S

When a US company has foreign subsidiaries the equity grants are usually done under Regulation S because the employees at the foreign subsidiaries are usually not a "U.S. Person." For the purpose of an exercise the definition of U.S. Person is different than the IRS and it is based on residency and not citizenship.

Has anyone received option grants as a U.S. citizen living abroad and exercised them before the company is publicly traded? While an expat living abroad is not a U.S. Person for this specific scenario I want to ensure there aren't compliance or other issues for the individual or the company.