Selectively caching models with cache_money

Question

Instead of doing this in the cache_money.rb initializer

class ActiveRecord::Base
  is_cached :repository => $cache
end

I want to be able to selectively cache only certain models (the reason being our User model breaks memcached because it's generally too large to be serialized properly).

class User < AR::Base
  is_cached :repository => $cache
end

This, however, throws an exception.

Any idea on how to do this?