Hi Truman,
Have you taken a look at the following Essential Diagram Knowledgebase Article:
How can I implement drag and drop from other controls on to the Diagram?
The sample included demnstrates how you can drag and drop from other controls on to the Diagram. This should give you an idea to do what you are seeking. If you have any further questions, can you post a small sample of what you are trying to do.
Regards
Arun