Can flash memory be used in place of RAM in microcontroller applications?
Flash is slow to write to, only accessible in blocks for erasing/writing, on many controllers (not sure about MSP430) slow to read data from (in contrast to reading instructions) and flash has limited write cycles (order of 100,000 times).

So the answer is: It can probably be done, but you shouldn't want to do it. 

Maybe an external I2C RAM is an option.