Wrap the imagex command in a bat file. At the end of your bat file, on its own line, put in the "exit" command.
Use the 'Execute file' action. For target, enter "start". For command-line parameters, enter "/w pathtobatfile.bat"
We use this method with 9.6 to show imagex progress. This also gets around the preferred servers bs that was added in 9.6.