you can actually add to the JSON of the aggregation using the "JSON input" under Advanced when editing the terms aggregation. That JSON will be merged into the JSON for the terms aggregation, so you can use it to set the execution_hint:
Though not sure if that possibility was already there in 4.5, since that version is quite outdated and not supported anymore. If the advanced JSON input does not exist at that time, updating to a more recent version should solve the issue.
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