Hi Gary,
The visual back that comes with a C11 can be replaced with a bigger version plus you could go one step further and used a Baader Click-stop unit that allowed the use of 2 inch accessories. It attaches directly to the 3.5 inch threads and made changing any 2 inch accessory a breeze.
http://www.optcorp.com/product.aspx?pid=154-13152
Or
Astrophysics sells a visual back for Celestron and Meade SCTs:
http://www.astro-physics.com/index.htm?products/accessories/focus_adap/focus_adap
If that doesn't work the parts are:
ADASCTLC (Celestron)
Cheers Mark