US Work Visa Question

Hey everyone
My friend is from France and he just got sponsored by his workplace for an H1B. He got his visa in France and now he is about to return. His work allowance starts on September 21 but he will try to enter as a tourist since he already had been living in US before this visa, with J1 visa for almost 2 years, and he has a relationship and he is sharing an apartment with his girlfriend etc. The questions is, he is scared that he will be denied entry to US because of the date on the visa. He is planning to leave the country and enter again right after September 21 to activate his work visa. Does anybody have relevant experience? You think this is going to work without a problem?

Thanks