In Cubase 6, I do this the same way you do it… but what I do is set up the sample editor and the project editor to be side by side. I zoom in very close on the project window at the area I want to warp (because I can see all the parts in context there). Then I use free warp in the sample editor to warp the event. It then updates in the project window as I do it, so I can match it to other parts doing that. You can also use Variaudio for this purpose, but see below for its shortcomings.
In Cubase 7 they’ve added another way to do this that to some people might be easier. Cubase 7 allows you to have multiple events open in the sample editor at once when using variaudio. Once all the events you have selected for editing are analyzed with Variaudio, you can see all the events you want to edit on top of each other. (Note this ONLY works with the Variaudio tab–not free warp). So in Cubase 7, you can use Variaudio to create and fine tune the segments, and then warp them using the other selected events as a guide in the same variaudio sample editor.
To be honest though, I’ve gotten so used to doing it the first way, it’s still faster for me. Using Variaudio to do horizontal (time) warping requires that you really do some detail work to set up the pitch segments exactly how you want them BEFORE you do any warping. But in free warp, because I know what I’m looking at, I can just quickly create warp markers exactly where I want them and move them accordingly.
That all said, with my particular projects (which often involve recording up to 24 different tracks of myself in order to create a choral effect), I’ve almost been able to improve my recording process to the point where I don’t need to do any warping at all. A good thing because… warping vocal parts is tedious and boring work, and it doesn’t sound as good. That’s neither here nor there though, sometimes it’s unavoidable, and that’s what the tool is for.