The objectStoreR package is VERY specific in that it only deals with CSV files. As a simple starting place, you could contact the author and ask if he/she is willing to write a objectstore.fetchToDisk() function that simply grabs an object and writes it to disk. That would allow you to interface with the vast majority of R I/O functions. Alternatively, you could modify the current get() function to save to disk. The GET() call is the place to make changes, most likely.