Since Lute took the perspective of them being on your 12, I'll take the perspective of them being on your six (which is what first came to my mind when I read your post).
You need to bleed their E before that climb to take the option away from them. Most of the great zoom-climbers aren't that great in sustained climbs, so, if you have a good sustained climber and want to use the verticle to your advantage, you need to get the zoom climber near your own E state before you begin the climb. You can do this by turning, scissoring or any of a number of other ways.
If you're already in a climb and you notice a zoom-climber coming up your six, the same principle applies. You need to bleed some E from him. I ran into this situation last night. I was in a 109G-14 with a zooming F6F closing on my six. At about D-800 I began a lazy spiraling climb, tighning it as he drew nearer. By D-400 he had his nose straight up, couldn't control it for the shot and had to break off. I didn't follow until too late because I was alone against ~10 F6F's but it would have/should have been a classic rope. This is only one, of course, of several methods you might be able to use depending on the specific situation.