When a user is logged into multiple gmail accounts, is there a way to let them select the account they want to use for mailto links?

When clicking on mailto links and selecting Gmail, it opens a stripped-down mail sender UI that a) doesn't make it clear what gmail account you'll be sending from and b) doesn't let you change the account.

You can change it manually in the URL by changing /u/0 to /u/1 or setting authUser, but is there a way to do this for my users with good UX?

I don't think there is a way to determine the from address from the "mailto," so maybe advise the users to create a Chrome profile for the Work account only, that way when the "mailto" is triggered it will only use that account.

However, if you are programming the "mailto" inside a web app or something, maybe forcing the Google account chooser from the code even if the user is login will do the trick.