breaking template parameter dependence

Hi All,

I have a class D<INT> which serves a small implementation purpose
(think for example D<INT> is Factorial<INT>). I don't want every class
that uses D<INT> to depend on template parameter INT. However I know
that I won't need more than say INT=5. So I do 2 things:
a) have D derive from a base class B (see below)
b) have a class Get with a member B& instance_of_B(unsigned int INT)
(see below). However I can't put references to B into an vector
because D<INT> is a singleton (non-copyable/assignable). do I have to
go through the trouble of creating a (copyable) wrapper around each
D<INT>& or is there an easier way (based on the code below)?

class B;//abstract class defining an interface

template<unsigned int INT>
class D: public B{
 public:
  static B& instance(){static D singleton; return singleton;}
};

class Get{
 public:
   Get()
    :r0(D<0>::instance())
    ,r1(D<1>::instance())
    ,r2(D<2>::instance())
    ,r3(D<3>::instance())
    ,r4(D<4>::instance())
    ,r5(D<5>::instance()){
      /* whatever else needed */
   };
   static B& instance_of_B(unsigned int i){
      // intended behaviour:
      // instance_of_B(0) returns r0
      // instance_of_B(1) returns r1
      // instance_of_B(2) returns r2
      // instance_of_B(3) returns r3
      // instance_of_B(4) returns r4
      // instance_of_B(5) returns r5

   };
 private:
    B& r0;
    B& r1;
    B& r2;
    B& r3;
    B& r4;
    B& r5;
};