I am not sure wether its exactly the same on your version as I am using 5.3 with EAP6.0 server, but I have to export my class implementing workItemHandler interface into a .jar and then copy it to the server library.
Then I have to tell the server to load the workItemHandlers on startup. Chapter 14.2.2 explains how to do this. Note that you have to restart your server to load changed work item handlers.
Within Guvnor you only create a custom work item definition and put your new custom service tasks into your process. You do not need to upload your workItemHandler within guvnor. Chapter 14.2.1 explains how to create a custom work item definition.
Thank you for answer, now I test your suggest