I think 'lying' is a bit strong. But I think that's because in this house it's seen as story telling, no more, no less and then dd takes from it what she wants. In the same way that I would no more sit at a magic show declaring 'they're tricking you dd, don't listen', I have never entered into a discussion about FC being a 'lie'. It's not a lie, it's a story.
That said, I do wonder at the sense in pinning the celebration of Christmas so much on the jolly, fat man and desperately trying to string it out/worrying that the magic could die. Because the magic of Christmas isn't about that one aspect. And I don't mean in a sanctimonious or smug way that children who believe are somehow oblivious to the other sides of Christmas but that it's falsely championed as the focus of Christmas when it's such a lovely opportunity to celebrate so much more.
Because FC is a 'story' (DD doesn't believe it to be literally true at all, never has), we also cover other aspects and stories. So dd hears stories of Yule and Pagans and Christianity and St Nick and Baboushka etc. And smug as I seem to sound when I talk about it, if you ask her about Christmas, at 4yo, the joy she takes from it is rarely about presents. She will wax lyrical about the stories and the songs, about seeing her family, about the traditions which have sprung up. We go to a friend's house to pick up logs and help clear out their stables as payment (dd gets a certificate to say she's a qualified stable elf, allowed to care for FC's reindeers if the need arises and she thinks it's brilliant). We bag up toys of hers (of her choosing) and clothes to give to the local shelter for other families, we go and volunteer at the soup kitchen (we do this throughout winter), we sing carols, go and look for Jack Frost, make decorations, make salt dough gifts for family, make up stories, dd puts on 'plays', we jingle bells outside her bedroom door and she pretends she doesn't know it's us. We do hang up a stocking and dd will get a few presents 'from fc' but most presents are from friends and family and dd has always known this. She also knows the fc presents are from us.
I never believed in FC either but I adored the magic and story telling and entered into the spirit of things. I loved and love Christmas.