how to add entry to contextmenu

Hy!

I do want to add an item to the contextmenu which appears when you
rightclick onto a contact item. This item should be my application.
And if possible the clicked item should be send to the application for
some further operation.

At the moment I have created a MenuBarButton which is connected to my
application. But then I would have to gray out the button as long as
my opened folder is not the one of the contacts. And besides, I won't
be able to send any contact item to my application this way.

So it would help me a lot if anyone had found out about what the code
has to look like to do either of these tasks meaning either

1) item in contextmenu: when being clicked the application starts (if
it isn't already running) and the contact is sent to the application
(if this is possible)

or

2) grayed out Button as long as the opened folder isn't the contact
item folder. When the button is clicked the "last selected item" is
being sent to the application which either starts or is running.

So if anyone of you had a sample of code it would help me a lot
solving my problem.

Thanks!
Stephan.