Registry Cleaner question.

Does anyone know if it is possible to run a registry cleaner (I have Wise Registry Cleaner) on a Hard Drive (with its own C Drive and OS on it, its a friend's PC hard drive from his computer that was acting up), while it is hooked up as an external to my main PC, if so, how is this done, because in Wise, I cant find a directory change function to change where i scan...