As a BT, I have personal experience with the issues discussed in this thread.
I grew up as an “active” Conservative, meaning we went to synagogue on a fairly regular basis. After I got married, we began to explore Judaism more and became more religious. At first, our growth was largely within the Conservative framework, as that is what I was raised with. I always had an attraction to Orthodox Judaism, but felt intimidated by it. In the town that we lived in at the time, there was a Conservative synagogue and a Chabad shul. Both were a considerable distance from where we lived (like 10-15 miles). We visited both, but started going more regularly to the Conservative one. Then I started wearing a yarmulke full time. Once, when driving home from the Conservative synagogue, I started to squirm in my seat. My wife asked me what was the matter. I said, “I feel like I need to take off my yarmulke.” She asked, “because we’re driving?” I said yes. We discussed the feelings, and decided that if we felt uncomfortable doing something while “looking Jewish”, then we must be doing something wrong. Starting the next Shabbos, we no longer drove.
I learned how to daven with an Orthodox siddur, and davened at home by myself on Shabbos. We lived like that for three years before B”H we were able to move into a frum community. Being able to go to shul is definitely better than davening alone, but once we began to understand what Shabbos was, to violate it by driving was not an option. I feel like I have a deep appreciation for shul now after those three years at home. I have no temptation whatsoever to talk during davening, and I tremble if given an aliyah.
Looking back, if I were directly rebuked for driving in an Orthodox setting when I still did so, it might have increased my fear of Orthodoxy and delayed our introduction into it. At the same time, someone who drives on Shabbos does not truly understand Shabbos. So instead of a direct rebuke, perhaps something more subtle would work better. Be very friendly. Be welcoming. And have an option ready for the person driving to be able to stay Shabbos in the community. And push it (cheerfully). Push how meaningful it would be, how honored you would be to have the person as a guest, etc. And act disappointed if turned down. I think that method would get the importance across without an unwelcoming stiff-arm.