You will need to run the power to the LCD via some kind of gate (logic level) and control that gate via the PIC or a timer.
Controlling it via a timer would be accomplished by having a retriggerable countdown based on the data lines. Once no data has appeared on the data line for a specified time.... turn off the power to the LCD.

The timer cct option would be a solution if you're running short of pins on the PIC

Does this help?
Des

>>> Brian Gracia <bgracia@RTRIPP.COM> 4/16/99 12:17:02 pm >>>
Hi All,

I want to controll my 4x20 LCD from a pic.  When the pic has not received
any keyboard input in say 5 min., I want it to power down (completly) the
LCD.  Blanking the screen may save some power, but being able to turn the
LCD on and off at will would help to prolong the life of it.

Any suggestions?

Brian Gracia