I've actually did this with 2 595's to be able to utilize all 8 bits of the LCD.
Since the transfer rate is so high, a delay must be added to the code of about 30us, this resulted in an average write speed of about 38-40us per byte sent to the LCD, as I have had troubles with missed letters when I tried to go down to the lowest spec of 37us delay (in total).
Here's my schematic (please ignore the resistor net as it wasn't tested. R3 resistor was also unnecessary as my LCD already has a 100ohm built in resistor):
*Click to enlarge.
Running prints of 80 chars starting with a random number:
And you can find a simple/limited library attached:
LiquidCrystal_SPI.zip (1.76 KB)