How to add shapes to a Combobox through code in Silverlight?

Question

Hi All
I need to add Some Shapes like Rectangle, Lines (with different thickness, giving an option to select from combo) to a combo box as item. So that whenever a particular shape is selected from the Combo box, I update the diagram/appliation accordingly.
For this Can anyone tell me how can I add rectangles/lines to a combo box?
Thanks & Regards
Padma