When exporting orgmode calendars to ics, ox-icalendar unfortunately produces ics files where all events are considered "BUSY".

As most applications seem to conform to RFC 2445, at some point or another, the following line seems to be added to the ics file:

              X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY

I'd like to have all my "all day events" turn out "Free", ie with the following line:

            X-MICROSOFT-CDO-INTENDEDSTATUS:FREE

How can I do that?
--René