open,closeとunwind-protectがあれば
安全なcall-withは各自で作れるよ

(define (call-with-io name proc open close)
　(let ((h (open name)))
　　(and h (unwind-protect
　　　　(lambda () (proc h))
　　　　(lambda () (close h))))))
(define (call-with-ole name proc)
　(call-with-io name proc
　　ole-object-create
　　ole-object-destroy))

(call-with-ole "Excel.Application"
　(lambda (h) ... ))

※ここでのunwind-protect書式
(unwind-protect try-proc finally-proc)