module Mail::Multibyte

def self.proxy_class=(klass)

Mail::Multibyte.proxy_class = CharsForUTF32
Example:

an example how to do this.
class so you can support other encodings. See the Mail::Multibyte::Chars implementation for
The proxy class returned when calling mb_chars. You can use this accessor to configure your own proxy 
def self.proxy_class=(klass)
  @proxy_class = klass
end