wpf dependency property show a dialog to select the value

Question

Dear all:
I have created a custom control with new dependency property (TagToSet) of type MyTag(id, name, value).
After adding this control to my window design, and going to the properties to set the value of the new dependency property. Here I want to open a dialog to select the Tag that I want (like the case when the dependency property is collection).
note: the Tag property is not a collection, and the required dialog should connect to a WCF service to list the available tag.
Here is an example of what I need



Thanks