If you go to a gym, you can use a stair climber. It is not the greatest thing. But climbing on a stairclimber is pretty similar in feel (at least to me) as to climbing a hill on a bike.

I think the suggestions on trainers should work. You just crank up the resistance and get out of the saddle. If you want the complete feel, you can incline the bike.

Remember, the hills out in Colorado on the roads generally do not get steeper than 7% and that is not really that terrible if you have low gears. I have taken riding vacations out in the rockies and done fine on long climbs and I live in Orlando, FL which is pretty flat.