Hi
You could try the following (note that changes to the path will not automatically update the expression value, you will have to use Update for External Change):
Now that you have the expression in the master, you can either create an attribute in the master and use the Relationship option in the Note editor to create a link from the drawing to the master, using "Object Attribute", or create a new interpart expression in the drawing to the master and refer to the interpart expression in the note editor.
Regards, Ben