Hi I am working with dual extrusion set-up.
I found from LCD you can't change active extruder, so I mod Marlin to allow manual extrusion (E0 or E1) from LCD.

Dual Extrusion.
Marlin 1.0.2 Modification for change active extruder from LCD.
It`s very simple.
Open Marlin on Arduino IDE.
Search UltraLCD.h
Add this two lines:
MENU_ITEM(gcode, "Activar E0", PSTR("T0"));
MENU_ITEM(gcode, "Activar E1", PSTR("T1"));
I added before this line:
MENU_ITEM(gcode, MSG_DISABLE_STEPPERS, PSTR("M84"));

After this mod you can choose active extruder E0 or E1 and move it from Move Menu>1 mm (0.1 mm)>Extruder


I love OpenSource.

I hope you find this useful.
Google+Post

I find it very useful!
Now, if I only find a way to retract faster.
It takes forever to change filament with a 500mm Bowden tube
-Olaf

My only solution so far is a hand written g-code that is permanently on my SD-card.

Maybe
MENU_ITEM(gcode, "unload filament", PSTR("your gcode for extract filament"));
MENU_ITEM(gcode, "load filament", PSTR("your gcode for load filament "));

This is not tested so be careful.
Keep your finger on power button while testing changes.