I do this on-screen in one of my processes. This method will compile all the previous comments into a single multi-line field (one at a time; each time a form with this code is launched, it takes the most recent comments and appends them to the older comments (that were already written to the field)). I want to be clear that I got help through Answers with making this work way back when, so this isn't my original work, but I couldn't say now who helped me at the time. 

I hope this helps!

$(document).ready(function () {
	  var com = $('#q85 textarea').val();
	//get previous comment
	  var com2 = $('#q87 textarea')[0].getAttribute('default-val');
	//get previous action participant
	  var displayname=$('#q89 input')[0].getAttribute('default-val');
	//get previous submission time
	  var submissiontime=$('#q88 input')[0].getAttribute('default-val');
	//get previous action
	  var action=$('#q86 input')[0].getAttribute('default-val');
	//combine the information together
	  var currentinfo=""; 
  		if(com2!=null){
          currentinfo=currentinfo+displayname+" at "+ submissiontime + ": "+ com2;
	      }	 

	//append to field that display the information
	if (currentinfo!=""){
	  com = com + '\n\n' + currentinfo;
	  $('#q85 textarea').val(com);   
	}
	  $('#q85 textarea').attr('readonly', 'True');
	});