If you truly do struggle getting both arms into motion at the same time and don't want to try and correct this, I think the best bet is starting with your toss and getting it fairly high. As soon as you've tossed you can get a feel for how to time your serving arm.
This reminds me of Sharapova's serve; although she does get both arms in motion at the same time, the high toss allows her ample time to get into the trophy pose (which she holds for quite a bit).
Careful with those super high tosses though. I always have trouble hitting service tosses after they've started dropping unless I'm intentionally going for a kick serve.