Well - i bought the same wrench and it worked out very well for me. I too had seized spoke nipples. I ended up using a propane torch to heat up the nipples and they broke free pretty easy. They were solid before i tried the heat.
If i remember correctly i used the #2 slot. I also had to hold the spoke with a small pair of vice-grips to prevent the spoke from rotating while i broke the nipple free (after heat).
Nipples - just wanted to type it one more time? :)