Instead of disconnecting the steering shaft at the u-joint, you can disconnect the steering rack coupler flange and reindex it on the splines of the pinion. That's what I did when I regreased my rack years ago. See this exploded view diagram from a Clymer manual I scanned back then
http://forums.pelicanparts.com/porsche-911-technical-forum/85404-steering-rack-rebuild-procedure.html
Between the splines on the pinion and the splines on the upper shaft at the steering wheel, there's enough fine adjustment to get the rack reasonably centered. The fine tuning at the tie rods finishes it off.
In all honesty, what's the big deal if the rack is not precisely on-center? Is there really a noticeable dynamic effect? I understand that your steering wheel rotation from center to left or right lock will not be the same, but so what. Who applies that much steering input to turn these cars? The ratio is quick enough that rarely is more than one rotation needed, even in the tightest of spaces.