Add custom properties to a Use Case

Hello,

i'm currently using Visual Studio 2010 Ultimate to create Use Case-Diagrams. Since i'm missing some properties of the Use Cases, i'm trying to add some custom ones.

Is there a way, to add custom properties (String, Int32 or boolean) to a Use Case in a Diagram? The properties should be displayed in the propertyWindow.

I allready found the following articles:

How to use the propertyWindow with an own extension:
http://msdn.microsoft.com/en-us/library/cc138529.aspx

How to add properties to a project:
http://social.msdn.microsoft.com/Forums/en/vsx/thread/14397e49-bf84-4d14-b356-cc4fbe82655a

So i'm able to create a VS-extension and, due to the possibility to add properties to projects, it may be possible to add properties to items (Use Case) as well...Or not? However, since i'm not a very experienced programmer, i'm not able to answer the following questions:

1. How do I get a reference to the Use Case, the user is currently working with?
2. How do I add a property to the Use Case, which is shown in the PropertiesWindow?

Thanks in advanced and best regards!