Sounds exactly like my Dp but he has agreed that once our bub is here he will change for the sake of them. He doesnt want to ruin christmas for them just because he doesnt like it, which i found to be a huge surprise but he loved christmas as a kid, im not sure what happeend to make him hate it now.

Maybe sit him down and say if not for himself for your daughter that he should atleast pretend to like christmas, why would he want his daughter to be the one kid that isnt excited about christmas, instead of thinking it as 'lying' to your daughter making her believe that santa is real but its what helps children with their imaginations, i remember as a kid being a true believer that a little fairy took our teeth when they fell out and left money, that a giant rabbit bounced around with his basket of easter eggs and santa claus flying in his sleigh around the whole world giving everyone presents, it was the best part of being a kid.

He doesnt have to wear stupid christmas hats or sing christmas carols but he can atleast set up a tree, have decorations and talk about santa with his daughter, help her write letters to santa and watch the excitement on her face afterall doesnt he want her to be happy??

These are some of what i said to dp to make him understand why its so important and he told me stories of what his parents did when he was a kid to make him believe santa was real.

Good luck!!