The basic premise is a simple one, let's use a beefy transistor as a digital switch to isolate the lower power GPO. Aniso drew up the following circuit to do just this:
N.B. this circuit should work for all gpo'S on MO character displays, I think GPO's on the graphic display work slightly differently and correspondingly need a slightly different circuit to the one shown above.
It's also worth noting that this circuit inverts the status of the GPO's, if the lower power GPO is off this circuit will be ON - great for controlling fans as the default state of a GPO is off, and you don't want the default state of your fans to be off!
So we have the circuit diagram, time to lay it out on stripboard...
Built:
Straped on to a wide voltage LK204:
...and controlling an LED strip light:
I used a pass through connector to power the LCD from the new board (so as to have just one power connector) - if you're using a normal voltage (5V) display you'll have to make sure you pass through the 5V line and not the 12V line or else you'll kill your display
More here - http://www.bit-tech.net/article/96/
Rob.