Is it possible to get the bucket interval of a histogram for bucket_script?

[prismatic]

I want to calculate (sum(my_document_field)/bucket_interval) for all buckets in a date_histogram. Its straightforward to calculate the sum with a sum_bucket aggregation, however I'm having trouble figuring out how to get the interval of the given bucket to calculate the value I'm interested in. The interval specified for the date_histogram may not be constant if 'week' or 'month', etc are used. Is there any way to calculate the interval for the parent bucket?

{
    "query": {
        ...
    },
    "aggregations": {
        "by_hour": {
            "date_histogram": {
                "field": "timestamp",
                "interval": "1h",
                "extended_bounds": {
                    "min": "now/d-5h",
                    "max": "now/d-1h"
                }
            },
            "aggregations": {
                "sum_raindrops": {
                    "sum": {
                        "field": "raindrops_seen"
                    }
                },
                "avg_scripts": {
                    "bucket_script": {
                        "buckets_path": {
                            "var_sum_raindrops": "sum_raindrops"
                        },
                        "script": "var_sum_raindrops / (?)"
                    }
                }
            }
        }
    }
}