How to replace a tube with only one quick stick?
I only ever use one tire lever.  


Deflate the tube
Use the lever to pull the tire lip over the rim opposite the stem
Slide (with a little force) the lever around the rim until the entire lip is free
Keep the other lip in the rim and remove the tube
Slightly inflate the new tube and place it in the tire
Shimmy the tire into place
Start seating the lip from the stem and work around to the opposite side
Use the tire lever (if necessary) to pry the lip back
Inflate the tube and make sure the lib is clenched all around


I suppose that there could be a reason that this is the wrong approach.  There may be a reason that using two levers is better.  BUT, I always use one and haven't noticed a problem.