If you're referring to the Shell Context Menu (the right-click window in Windows Explorer), you cannot. You can add to the menu that will be displayed for all .exe files, but not for an individual one.
You could register a context menu handler for all executables, and then filter the filename passed to see if you needed to handle it or not, but this would mean that for every one of the hundreds (or thousands) of executable files on your machine, your filter would run on the slim chance it was your application that was right-clicked.
A possible workaround would be to put a file with a custom extension in your service's folder, and add a context menu handler for that file instead. When that file is right-clicked, the menu items would simply call your service with the appropriate command-line parameters.
(Of course, the best solution is to use the Control Panel's Services applet to manage your service, which is what it's designed specifically do do.)