This tool uses jquery library to handle AJAX request to custom web service. You not need to modify anything on custom web service.
It's very easy and only few steps to accomplish installing this tool on Microsoft CRM.
Here are screenshots of this tool.


Custom menu on grid toolbar and detail form



Select workflow and query result (advance search) to execute. You would see there is a link, after drop down list, to popup the detail page of selected item.
Confirm dialog appears after the user hit execute button.

Progress bars represent underneath the execute button. There are two progress bars for retrieving entities to be executed through and execution request.

Even though the progress bars show as finished but it's not. It just finished requesting to execute throughout the specified entities. You have to monitor eash request status yourself as showing in the screenshot.
I'll provide you deployment instruction of this tool SOON!