What about extending object's memory representaion. Like adding some
fields to RClass.

	rb_extend_value( VALUE Val, unsigned long extSize );   //
relocates RClass structure pointed by Val. 
							// Resizes it to
be longer by extSize VALUES
	rb_get_value( VALUE Val, unsigned long offset );	//
retrieves offset'th VALUE from the extension area.
	rb_set_value( VALUE Val, unsigned long offset, VALUE Val );
// set soffset'th VALUE to Val.

This would help storing some data when creating class and instance
variables does not suite.