Date_histogram on multiple fields


We are making changes to schema to have a new index(w/ new schema) but still support old index (w/ old schema) for search.

We currently have date_histogram computed on a date time field as given below.
"date_histogram": {
"field": "closeDt",
"interval": histo_interval

where closeDt is time in milliseconds and histo_interval is week/month/hour interval range

With new schema also to be supported, the new schema has closeDt in a different json structure like
cs.common.closeDt (also time in milliseconds).

how can we have the histogram computed on both the fields (w/ same data type) ?

Thanks, Vinoth