Use script on count metric

Hello,
How could I use a script when counting?
e.g:
{
“alias”: “”,
“datasource”: “”,
“hide”: false,
“metrics”: [
{
“script”: {
“inline”: “(_value*(12*60000))/${__interval_ms}”
}
},
“type”: “count”
}
],
“query”: “”,
“timeField”: “”
}

where _value is the counted value.

Thank you!