You can't use flash ROM as RAM (it's called ROM for a reason). Well, you can, but only until it wears out. It is not intended to be used as RAM, sorry.
Do you really need flash? If you are constantly writing new data, why do you need it to be non-volatile? Maybe you should have RAM PLUS a flash device which you only write to occasionally. If you REALLY need non-volatile RAM, you should consider using battery-backed RAM, but I don't believe they make serial, battery-backed RAM,