Alternative to copy-in/copy-out?

I am just starting out with UFFI, and it looks very useful.  I have
ported a small amount of ACL-specific foreign interface code, mostly
to Fortran, to UFFI.

When using the ACL interface I could directly pass CL objects to and
from foreign code.  I am looking for the analogue in UFFI.
In c-test-fns.lisp there is a function

(defun t2 ()
  (let ((vec (make-array +double-vec-length+ :element-type 'double-float)))
    (dotimes (i +double-vec-length+)
      (setf (aref vec i) (coerce i 'double-float)))
    (half-double-vector +double-vec-length+ vec)
    vec))

which seems like it should do what

(defun test-half-double-vector ()
  (let ((vec (uffi:allocate-foreign-object :double +double-vec-length+))
	results)
    (dotimes (i +double-vec-length+)
      (setf (uffi:deref-array vec '(:array :double) i) 
	    (coerce i 'double-float)))
    (half-double-vector +double-vec-length+ vec)
    (dotimes (i +double-vec-length+)
      (push (uffi:deref-array vec '(:array :double) i) results))
    (uffi:free-foreign-object vec)
    (nreverse results)))

does, and is much simpler, and should be more efficient.  However,
it doesn't work for me.   

Is there a way to avoid copy-in and copy-out when making foreign
calls through UFFI? 

Thanks for ideas.

Liam