the "say it right" program has vocalic /r/ stories, etc that may be helpful...
also, teaching student to blend sounds may help...such as "oh" --- "er" for vocalic "or"; say each sound slowly, then slowly blend; pick up pace until you say the vocalic /r/ naturally......"ee" - "er" for "ear" / "ah" - "er" for "ar" / long "i" - "er" for "ire"