Best thing to do is ask for the manager, be polite explain the deal, say you had to be somewhere and could not turn around.

Ask him what they will do to fix the problem at hand. (First rule of negotiating never offer the solution, thee who speaks first looses). If they do not offer something explain that your car did not have this pull before hand and ask again what can be done to fix it ? Most likely he will say a alignment check so act as if they are going to do this chack for free. Playing dumb goes a long way.

On a side note the pull can be from a few things. First the air pressure could be different on either side of the car. Or they may need to swap a tire from one side of the car to another to cure the pull. We had this problem all the time when I was a tech.. Some tires will just pull to one side due to casting problems. putting that tire on another side could fix the problem.

Good luck and stay calm untill all else fails.