Since your job contract is only one year and not permanent, so you won't be able to go for employment-based petition. If you are qualified, you may try NIW or EB-1 which don't require sponsorship. But this is for H1 visa that most people hold. I heard that for your G4 visa, you need to get a kind of form apporved by Dpeartment of State before transfering to an immigrant visa. Better to cousult a lawyer.