Why use refractor if you can get Reflector from Red-Gate for about $35.
The other thing is if your want to implement a custom cache why don't you just implement all the stuff that makes ObjectCache abstract?
Another option is to use the MemoryCache type and derive from that.
You could of course consider to do some R&D in this namespace here:
http://msdn.microsoft.com/en-us/library/dd985642.aspx[
^].
If you run into any difficulties leave a comment.
Happy coding!
-MRB