please see for reference the text of the Convention - http://www.irs.gov/pub/irs-trty/swiss.pdf - page 30:
ARTICLE 19 Government Service and Social Security
1. a) Salaries, wages and other similar remuneration, other than a pension, paid by a Contracting State or a political subdivision or a local authority thereof to an individual in respect of services rendered to that State or subdivision or authority shall be taxable only in that State.
b) However, such salaries, wages and other similar remuneration shall be taxable only in the other Contracting State if the services are rendered in that State and the individual is a resident of that State who:
i) is a national of that State; or
ii) did not become a resident of that State solely for the purpose of rendering the services.
So - if you either did not render services in the US or are not a US resident for tax purposes - your compensation should be taxed in Swiss only.
See also the IRS publication 901 - http://www.irs.gov/pub/irs-pdf/p901.pdf - page 32:
Income, other than a pension, paid by Switzerland or its political subdivisions or local authorities to an individual for services performed for the paying governmental body is exempt from U.S. income tax. However, the exemption does not apply to payments for services performed in the United States by a resident of the United States who either:
-- Is a U.S. citizen, or
-- Did not become a U.S. resident only to perform the services.
Pensions paid by Switzerland for services performed for Switzerland are exempt from U.S. income tax unless the recipient is both a resident and citizen of the United States.
So far - you may claim Tax Treaty exemption because services were performed outside the US.
Let me know if you need any help.