The same way you built StackOverflow. Find a blog that is very popular with those demographics and convince/Cajole those bloggers to review the site.

I'd think Superuser would be a good topic on LifeHacker.

Don't know many blogs focused on the admin types though.

Also, maybe if you posted some of the more popular (and general interest) questions to the appropriate Reddit, Digg, or Technorati subsites you'd get some traffic from there.

I tried that once for one of my questions on SO (Tells of a Novice Programmer) and got a decent bump in views the next day.