Sorry, I don't use simulink. Submissions for this section are gratefully accepted.
Ikaro Silva contributed this answer:
A quick way to do this is to use a screen capture of the model. To take a screen capture under Windows, press Alt+PrintScreen to copy a bitmap of the current window to the clipboard. Then paste it into your document using Ctrl+V or RightClick->Paste.
In R12.x you can also copy the model to the clipboard from the Edit menu within Simulink.
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