I knew I'd read another one and I found it but it turns out it's House/Cuddy but while I was looking for that I pulled up a whole list of 'A Christmas Carol' stories - here (https://www.fanfiction.net/search.php?ready=1&keywords=christmas%20carol&categoryid=1968&genreid1=0&genreid2=0&languageid=0&censorid=0&statusid=0&type=story&match=&sort=&ppage=1&characterid1=0&characterid2=0&characterid3=0&characterid4=0&words=0&formatid=0) .

There's a story where Wilson goes back in time, grabs House from John and raises him from childhood. I liked it but it's um... not a happy story. I don't have a link handy but if you're interested I could probably find it somewhere.