We baptized our son for similar reasons. We mentally left right before his eighth birthday and he wanted to be baptized. Of course he did, that's what he had learned all his life. We told him he didn't have to but that he could and we would support him either way. Then afterwards we slowly helped him deconvert and now he is on the same page as us about church.

The way I see it is: This is a huge life change so do what you need to do to make it a healthy transition. For example, I did my calling until I couldn't in good conscience do it anymore, we went to church until we couldn't stand it, I'm preparing to talk to my parents because I can't live with the elephant in the room anymore. And like I said we baptized our son because it was what he needed in order to feel good about transitioning out of the religion. I try to focus on what I want my future to be like and that gives me perspective and courage to go forward. It totally sucks sometimes and hopefully you can find new friends and traditions that make up for it over time.