It's a penny-farthing; sorry, but I'd have thought that this would be obvious. Really.

Seriously, I see that my original post was a bit ambiguous. I'm not building a new wheel; I'm adding tension to a factory built CXP-22/Ultegra 6600 rear wheel. I want to add a bit of tension to all of the spokes without throwing off the dish. Now, when I say the rim is not offset, I mean that the spoke holes are not drilled asymmetrically as they are on some rims (aeroheads are like this, yes?) to mitigate the disparity in spoke tension between the drive and non-drive sides. Does that help?