Very carefully.

Basically I'm doing it by simply not letting apt update any kde packages to 4. Unfortunately I also know that eventually dependency needs will force my hand (it's already making me hold back a couple of fairly important non-kde packages). I've been wondering what to do when that time arrives, and it looks like it's getting pretty close. I've already been forced to go through the move on my other machine...which is the only reason I don't use it as my main system, since it's actually more powerful than this one.

But that's all I'll say about it here, since it's way off topic. Not to mention that I'll be in full-on rant mode very quickly if I don't stop myself now.