Pop-up messages on Agile boards

[Saida]

Hi! 

I want to add a custom listener to check the Sprint value update and pop-up some message to user. 

import com.onresolve.scriptrunner.runner.util.UserMessageUtil

///
UserMessageUtil.error("Error message")

The problem is that UserMessageUtil class methods are not working on Agile boards due to the bug SRJIRA-3465. 

Is there any other way to show a message? Scriptrunner Script Fragments are able to show flags but I did not find the way to do a similar thing from groovy script.