Go to the Comps section in Reports Now™. If you have any comps added here, you'll see a button under each comp address: Copy Comparable.

Clicking this will reveal a new window prompting you for a property address. Enter the property address you want to use for this new comp and click copy.

All the details from the original will clone over to the newly added comp:

Please Note: This only applies to sales comps. Rental comps cannot be cloned at this time.