I got an offer for an assistant professor position in the USA starting on September 1st. Classes start on August 21st. So I am expected to start teaching at the university before I'm actually employed. Until this point, ok, I don't mind.

However, as I am a foreigner, I can enter the USA with my H1B visa (work visa sponsored by the university) only 10 days before the contract starts. 10 days before will be August 22 (remember: classes start on August 21!). I would prefer to enter the USA before August 22, to organize my life before I start the full-time position (rent a house, buy a car, hire internet, electricity, do all the moving, etc).

Is it possible to ask the university to sign my contract starting 1 or 2 months before September 1st so I can enter the US before August 22? I wouldn't ask for more salary for that 1st year, of course. It will be only an administrative solution for me to have a visa earlier. 
Is it possible?