This is easy actually. See below workflow. What you have above is a folder action. If you copy what I have below, change the external hard drive location and Save As an app, then all you have to do is click on it and it will do exactly what you want.
Here it is:
Or you can download the one I made. Double click on it and it will open in Automator and then change the external drive and then Save As an App and call it what you want.
Here is the download:
http://s3.amazonaws.com/f.cl.ly/items/2S2N0E3B1Z3X1U3E3X1C/Eject%20and%20Sleep.w orkflow.zip?AWSAccessKeyId=AKIAJEFUZRCWSLB2QA5Q&Expires=1362885484&Signature=SuW r9p786dR4vS9nzyX%2FCtiO%2B7w%3D&response-content-disposition=attachment