(defclass substandard-method (standard-method) ())

(defgeneric frobnicate (thing))

(defun test ()
  (let* ((gf (fdefinition 'frobnicate))
         (lambda-list `(thing))
         (lambda `(lambda ,lambda-list (print thing)))
         (method-lambda (c2mop:make-method-lambda
                         gf
                         (closer-mop:class-prototype
                          (find-class 'substandard-method))
                         lambda
                         nil))
         (method (make-instance 'substandard-method
                                :function (compile nil method-lambda)
                                :lambda-list lambda-list
                                :qualifiers '()
                                :specializers (list (find-class t)))))
    method))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

CL-USER> (defvar *method* (test))
*METHOD*

CL-USER> *method*
#<SUBSTANDARD-METHOD (#<SB-PCL:SYSTEM-CLASS COMMON-LISP:T>) {10148D5643}>

CL-USER> (add-method #'frobnicate *)
#<STANDARD-GENERIC-FUNCTION COMMON-LISP-USER::FROBNICATE (1)>

CL-USER> *method*
#<SUBSTANDARD-METHOD COMMON-LISP-USER::FROBNICATE (T) {10148D5643}>

CL-USER> (c2mop:generic-function-methods #'frobnicate)
(#<SUBSTANDARD-METHOD COMMON-LISP-USER::FROBNICATE (T) {10148D5643}>)