How can I reshape my data before I turn it into a histogram?

Imagine that I have a visits index that contains documents of type 'visit' that look like the following:

{
               "id": "c223a991-b4e7-4333-ba45-a576010b568b",
// other properties
               "buildingId": "48da1a81-fa73-4d4f-aa22-a5750162ed1e",
               "arrivalDateTimeUtc": "2015-12-22T21:15:00Z"
}

The following function will return a histogram which returns buckets of visits for each day in the given range according to the given time zone.

    public Bucket<HistogramItem> Execute(MyParameterType parameters)
    {
        var buildingFilter = Filter<VisitProjection>.Term(x => x.BuildingId, parameters.BuildingId);
        var dateFilter = Filter<VisitProjection>.Range(r => r
            .OnField(p => p.ArrivalDateTimeUtc)
            .GreaterOrEquals(parameters.EarliestArrivalDateTimeUtc)
            .LowerOrEquals(parameters.LatestArrivalDateTimeUtc)
        );

        var result = _elasticClient.Search<VisitProjection>(s => s
            .Index("visits")
            .Type("visit")
            .Aggregations(a => a
                .Filter("my_filter_agg", f => f
                    .Filter(fd => buildingFilter && dateFilter)
                        .Aggregations(ta => ta.DateHistogram("my_date_histogram", h => h
                            .Field(p => p.ArrivalDateTimeUtc)
                            .Interval(parameters.DateInterval) // "day"
                            .TimeZone(NodaTimeHelpers.WindowsToIana(parameters.TimeZoneInfo)) // This is a critical piece of the equation.
                            .MinimumDocumentCount(0)
                        )
                    )
                )
            )
        );

        return result.Aggs.Nested("my_filter_agg").DateHistogram("my_date_histogram");
    }
}

// Returns [{Date: 12/22/2015 12:00:00 AM, DocCount: 1}]

Now imagine that I changed things up a bit. Imagine that I added a new field to the document:

{
               "id": "c223a991-b4e7-4333-ba45-a576010b568b",
// other properties
               "buildingId": "48da1a81-fa73-4d4f-aa22-a5750162ed1e",
               "arrivalDateTimeUtc": "2015-12-22T21:15:00Z",
               "departureDateTimeUtc": "2015-12-23T22:00:00Z" // new property
}

And assume that I want to return the following:

// Returns [{Date: 12/22/2015 12:00:00 AM, DocCount: 1}, {Date: 12/23/2015 12:00:00 AM, DocCount: 1}]

because the visit spanned two days and I want a date histogram which records one unit for each day that a visit spans.

How would I do this with NEST/Elastic Search?

Note 1: Unless someone convinces me otherwise, I don't think would be a good idea to collect all documents in the range and perform the aggregation/bucketization and date histogram in the middle-tier (or C# layer).

Note 2: The time zone aspect of this problem is critical because I need the counts to be bucketized according to the given time zone.