better way?

[tmoran@acm.org]

I'd like to do something like:
  package Outer is

    type Inner_A_Thing_Type;
    type Inner_B_Thing_Type;

    package Inner_A is
      type Thing_Type is ...
      procedre P(X : access Inner_B_Thing_Type);
    end Inner_A;
    subtype Inner_A_Thing_Type is Inner_A.Thing_Type;

    package Inner_B is
      type Thing_Type is ...
      procedre Q(X : access Inner_A_Thing_Type);
    end Inner_B;
    subtype Inner_B_Thing_Type is Inner_B.Thing_Type;
    ...
  end Outer;

but the "subtype" instead of "type" prevents it.  Suggestions?