Watcher input extract fields

OH YEA! THANKS! It appears that breaking the query params into another element worked!

For posterity, here is a summary of what worked on my aggregation.
PUT http://{{host}}/_watcher/watch/cal_tpv_agg_watch

{
  "trigger" : {
    "schedule" : { "interval" : "3600s" } 
  },
  "input" : {
    "http" : {
      "request" : {
       "host" : "elasticserver.dev.mycorp.com",
       "port" : 9200,
       "headers": {
            "Content-Type" : "application/json",
            "Accept" : "application/json"
       },
       "params": {
            "search_type" : "count"
        }, 
       "path" : "/cal-root-2016-03-07/logs/_search",
       "method": "post",
       "body" : "{ \"aggs\": { \"tpv\": { \"terms\": { \"field\": \"payload.m_merchant_account_number\", \"order\" : { \"total_volume\" : \"desc\" } }, \"aggs\": {  \"total_volume\": { \"sum\": { \"field\": \"payload.usd_amt\" }}}}}}"
      }
    }
  },
  "actions": {
    "log": {
      "logging": {
        "text": "Watcher ran {{ctx.watch_id}} at {{ctx.execution_time}} with payload {{ctx.payload}}"
      }
    }
  }  
}

It is now returning the aggregation response in the watcher response payload.