You can add any RAW image to your existing document as a Smart Object. Just use the Place command (under the File menu) and navigate your way to the RAW image. When you choose the RAW image, Photoshop will first open Camera Raw so you can process it. When you click Open in the Camera Raw dialog, it will place itself into your document as a Smart Object (and it will have a bounding box around it so you can determine the size you want it to appear within your document). Once you’ve sized the placed image, press Return (PC: Enter) to lock it into position. If you need to make any edits to the RAW photo after it’s placed into your document as a Smart Object, just double-click on the Smart Object’s thumbnail in the Layers palette and your RAW image will reopen in Camera Raw. Make your changes, click OK, and it will automatically update in your main document. Sweeeeeettttt!