I've been wondering the same thing. The answer I seem to have so far is that no, you can't. And, of course, you don't know whether your server is still on the Wonder or has been reassigned to the Magic. I "heard" somewhere that about 75% of the Wonder staff stayed on the Wonder when the Magic went online.
Anyway, I've also heard that it might not hurt to call
DCL about 3 weeks before the cruise to request your server. I may try that as well. If that doesn't work, after you board on the first day, take your dining tickets to the place they do dining changes and you might be able to do it there. I'd recommend doing that as soon as you're able.