A couple of things you can do, similar to the bomber instructions I've given out in the past. First, go into your offline arena setup and turn off "protect friendly objects" as this will allow you to bomb stuff on your own field and destroy it. That gives you some good feedback though you will feel the impact of destroying stuff so you will want to exit-re-enter your arena to fix the field or move from field to field.
Secondly, you can improve your rate of climb by using the Wind. There is a "rise" factor to wind that can cause a significant updraft that will make you into a rocket-ship in climb. First, take off and level out to pick up a little speed, then turn off the autopilot and turn on the "Rise" wind setting to the max of 127. You can find that under settings on the clipboard. Don't close the wind settings window, get to altitude and press "no wind" to cancel the wind so you are back to normal.... then bomb away.
The reason you can't use autopilot is because it tries to hold your atltitude and thus you will start a death dive into the upward wind and eventually it can kill you. You can use the auto-angle autopilot mode (turn off X and press SHIFT-X immediately) as this simply holds the angle and would not dive... then turn the rise wind on.
Hope that helps. You can use the same method for bomber practice and it obliviates the requirement for long climbs.
