You just need a Canon T-ring adapter: it's has a Canon lens mount on one side, and a thread on the other side that screws onto the field flattener. Most astro shops should stock them, such as:
http://www.bintel.com.au/Astrophotog...oductview.aspx
http://www.andrewscom.com.au/site-co...-longperng.htm (see bottom of page)
http://www.myastroshop.com.au/produc...sp?id=MAS-052D