[racket] syntax-case in r5rs

How can I import Racket's versions of define-syntax and syntax-case into
r5rs?
I tried the following:
 
#lang r5rs
(#%require (only racket define-syntax syntax-case))
(define-syntax (a stx) (syntax-case stx () (_ #'here)))
 
Gives error: macro-transformer: only a `syntax-rules' form is allowed in:
(syntax here)
 
r5rs is not my choice. I use it for Phil Bewig's programming praxis.
 
Thanks, Jos
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