for/first in terms of for/fold without let/ec

gistfile1.txt

#lang racket
(define-syntax (my-for/first stx)
  (syntax-case stx ()
    [(_ (for-clause ...) . defs+exprs)
     (syntax/loc stx
       (let-values ([(val _)
                     (for/fold ([val #f] [stop? #f])
                       (for-clause ... #:unless stop?)
                        (begin 
                          (define x (let () . defs+exprs))
                          (values x #t)))])
         val))]))

(my-for/first ([x '(1 3 5 7 4 6)]
               #:when (even? x))
              x)