I worked at a McDonald's when I was a kid & had a similar issue. Easiest thing to do is just stick with what they want you to say, but change it up slightly to make it easier to get out. For instance, instead of starting off with "thanks for choosing.......", maybe try saying "hi, thanks for choosing.....". Or "hey", or "welcome", whatever makes it easier for you. You're still meeting the intent of what they want you to do, so there shouldn't be any issue from management.