Declaring private packages to instantiate generics?

["Markus Schöpflin" <no.spam@spam.spam>]

I just found myself wanting to write the following code, which Gnat doesn't like:

---%<---
package FOO is
   procedure P;
end FOO;

package body FOO is
   package BAR is new SOME_GENERIC_PACKAGE;
   procedure P is new BAR.P;
end FOO;
--->%---

Can I somehow provide the body of P without writing a procedure which just 
forwards to an instantiation of BAR.P, IOW without having to write:

---%<---
package body FOO is
   package BAR is new SOME_GENERIC_PACKAGE;
   procedure BAR_P is new BAR.P;
   procedure P is begin BAR_P; end;
end FOO;
--->%---

Regards,
Markus