First, look at the space between the smallest cog and the inside of the frame. you need to have at least 2 millimeters of space. If so, loosen the nuts on the left (no cog) side of the hub and take it apart. clean the grease off the axle and look at the assortment of cone, spacers and nut on the "cog end" of the axle. somewhere in that collection is a washer of normal thickness, about 1mm.

Take apart this assortment until you reach this washer, remove it and reassemble the spacers and nut. Be sure to back off the cone a turn or two so the amount of axle sticking out beyond the nut is the same, or your quick release won't tighten. Now grease everything up and reassemble the whole hub putting the washer you removed fron the cog end of the axle onto the no cog end. adjust the bearings and tighten everything down.

What this does is move the entire wheel over to the right by 1 millimeter. That means you have to move the rim 1 millimeter to the left to recenter it. This, of course, means your wheel will have 1mm less dish. doesn't sound like a lot, does it? But it is less. In fact, you can subtract 1 millimeter from the longer spoke, and add that millimeter to the length of the shorter spoke. If you have a six or seven speed freehub, since there is only two millimeters difference between the left and right side spokes, BOTH sides of the wheel will now be able two use the same length spoke.