[plt-scheme] mixin macro for classes?

Hey everyone,

I have would to write a set mixins for the pasteboard class using the 
mixin macro.


(define snapping-pasteboard-mixin
   (mixin (?some-interface-that-doesn't-exist?)
	 (?an-interface-of-some-sort?)
       (rename (super-interactive-adjust-move interactive-adjust-move))
       (override interactive-adjust-move)
       (define (interactive-adjust-move snip box-x box-y)
         'more-will-go-hear
         (super-interactive-adjust-move snip box-x box-y))))

(define snap-pasteboard% (snapping-pasteboard-mixin pasteboard%))

The key problem being that interactive-adjust-move is not in any
interface that I am aware of.

Is this possible/desirable?  Do I have to define my own interfaces for 
the pasteboard% class in order to do this?

Or should I just write a simpler version of mixin?

Thanks,
Bruce