Your sponsor has a vested interest in your doing well at the company-site interview. This person, who may have initially been a screener, is now an includer. You will be the personal representation of what they view as a potential new employee. In a way, their professional reputation is on the line whenever a new person is brought back to the company-site. No one wants to hear the dreaded, "Why did you invite that person back?"
So take advantage of this turn of the tables. The person who was against you is now for you. Be prepared to ask some questions:
"Who will I be meeting with?"
"What is this person's background?"
"What will they be looking for in the interview?"
"Will there be any other activities scheduled during the day?"
"What can I do to prepare myself further for your company?"
"Can you send me additional material about your company?"
You have a free opportunity not only to ask the questions, but to ask for recommendations. You will get a true insider view of what it takes to be successful at your company-site interview. Your sponsor is now your advocate. Build your personal connection to your mutual benefit.