Lambda the Ultimate

Ada 95 provides a mechanism with tagged and type'class to allow dynamic dispatch. So if one has:

procedure something (O : basetype'class) is
begin
enact (O);
end something;

then as we all know, with the appropriate redefinitions of enact () for the subtypes of basetype, we have dynamic dispatch.

But what about deallocation ? I want to declare:

type handle is access all basetype;

procedure dispose (ptr : in out handle);

and can't see how to make this deallocate the correct object. Obviously, one can dynamically dispatch on ptr.all but it seems impossible to solve the complete problem without an unchecked conversion. Anyone ?