Embedded OmniGraffle Objects Without Margin?

How can I create an embedded OmniGraffle object in my document, without it having a margin?

When selecting a group of objects I perform a “[Right Click] >> Copy As >> PDF” (or PNG). This embedded a copy of the objects into the document, which I can then crop. However, it also creates a margin around the embedded object, which I do not want. Can I remove this margin?