(set-macro-character #\!
                     (lambda (stream ch)
                       (declare (ignore ch))
                       (let ((*package* (find-package (read stream))))
                         (read stream)))
                     t)

(defpackage "SOME-PACKAGE" (:use))
(quote !some-package (xyz "a" cl-user::xyz))
--> (some-package::xyz "a" common-lisp-user::xyz)