Trakt has a recent history ical feed on your profile history screen. Mine seems to go back a week, or 60 entries, which I think should be enough for Exist to collect stats every day. I just set this up, so hopefully it works.
That’s for sure a possible workaround, but it would be perfect, if it could be an own attribute instead mixing it with appointments. Not to hijack the Trakt scope here, but with the iCal integration should be used to differentiate between multiple real calendars (like Private, Business..).