From personal experience
I know this thread is long dead but for those searching the forums... if you have a tight fitting tire, like I did with an old Continental wire bead tire, try getting a cup of really soapy water and covering the rim and tire where it's tight, and the ends of the levers with.
I was trying to fit a tire for over an hour and it was impossibly tight in the last 2 or 3 inches. Read on the forum that someone suggested soap, and it worked, so try it!