Depending on the liner quality, just riding them will help mold them. If they are really good quality liners, they will last with a bake or two. From what Angry said, sounds like the shop gave you the perfect advice.
I always go to a boot fitter anyways for new boots., I don't get head molded, but I have him add a little cork heel lift to my superfeet red insoles, and a top-of-the-instep pad to help my slightly smaller foot from moving around. He always does it for free and I tip him.
Boot fitting is not often done for soft boots, but I think for some people it could help