In the end everything that is storage can also be used as memory. You could print it to paper and scan it back in when the cpu requires it (and write a memory interface to do so).. It would just be terribly slow if you don't use something like DRAM
You can use a ramdisk to use memory as storage. And if it's volatile memory just be sure to never power it down.
Ignoring the applicability of it of course.