Just go for general bike fitness. If the grade isn't extremely steep, you shouldn't have too much trouble with long climbs. In Ohio, the big climbs are 400 feet and 2 miles long, and most are 300 feet and 1 mile. To me, a 2800 foot climb doesn't seem like 7 or 8 times bigger. It's partly that I'm pacing, since I have no idea how long it'll take, and the scenery is usually spectacular--I'm having a great time on the climb.

I can't help you with high elevation climbs, up toward 10,000 feet, though.

I always use a heart rate monitor, which really helps in pacing up the climbs. A few years ago, before my first big climbing ride, I rode a rolling country road for 30 miles out and back, with no stop signs. I was trying to hold my "ride fast for an hour" heart rate as much as possible for the whole distance, simulating a long, steady climb. That was useful, but now I just do my usual riding, and try to do a good amount of miles on the weeks before the big ride.

Here's an example, up to Mt Mitchell from Asheville, with 8000 feet of climbing in 64 miles.