When looking at a watchlist, a "CA" tab is added to take you to your Special:CentralAuth page. There, the links to individual wikis are changes to actually link to your watchlist on that wiki.

Importation

This script can be imported to global.js by adding:
mw.loader.load('//meta.wikimedia.org/w/index.php?title=User:DannyS712/Watchlist.js&action=raw&ctype=text/javascript');