It seems not possible right now ;-(
There are some workarounds, such as:
- Use clone filter (https://www.elastic.co/guide/en/logstash/current/plugins-filters-clone.html) and mutate filter
- Use 3 logstash instances !
- 1 ==> output in queue
- 2 ==> input from queue ==> output to ES
- Write your own plugin, it's dramatically easy, and the best way to fit your needs