foo.clj

(require '[boot.core       :as core]
         '[boot.file       :as file]
         '[clojure.java.io :as io])

(let [tmpd (core/mktgtdir!)
      srcs (->> (core/src-files+) (core/by-ext [".scss" ".sass"]))]

  ;; make hardlinks for all the scss and sass files into the tempdir
  (doseq [in srcs]
    (let [rel-path (core/relative-path in)
          out      (io/file tmpd rel-path)]
      (file/copy-with-lastmod in out)))

  ;; given some file with path p in one of the user's source or resource dirs,
  ;; you can find the corresponding file that's been copied to the tempdir above
  ;; like this:
  (let [file-user-refers-to (io/file p)
        relative-path-of-file (core/relative-path file-user-refers-to)
        corresponding-tempfile (io/file tmpd relative-path-of-file)]
    ;; here you can tell sassc to compile corresponding-tempfile
    )
  
  )