Reply to Side Conversation via API on behalf of end user

Is there any way to reply to side conversation on behalf of end user?

I'm able to create/comment tickets via Request API on behalf of end user but it seems that side conversation API is restricted for Agents only. 

I was trying to workaround that by setting the message.from attribute of my payload to the end user email and name but the API (link) ignores it and the author (from) of the reply was my admin user :/