The only photo I could find of piggyback is the wrong way around Lol. Usually the main telescope is in the main mounting rings and the camera on top. Mine is the other way, but I think it may still give you the idea. In this image I'm taking the photo with the camera and 400mm tele lens and guiding with the white telescope.
This page may help too, but the field of view is for 35mm film cameras.
http://www.astronomy.com/asy/default.aspx?c=ss&id=12