I use BAW's technique.
I get my plane into position with the slew, and then speed up time to 16x, and just keep hitting the pause key until I have a decent strike.
Then with the game in pause, you can mess with the weather, time of day, camera angle and plane type, and the lightning will still be there.

Just don't un-pause the game until you're done.

My method is a bit different:
Slew the plane into position.
No speed up time whatsoever. Regular speed.
Keep the plane in slew. Putting it in pause will stop the navigation lights from flashing as well as the lightning strikes. You can still mess with the weather, time, camera angle and plane type while in slew mode.
If you use F1View, it can store up to 1000 shots (000 to 999). After I do what seems like a lot of pressing print scr, I'll minimize FS and take a look at what I have. I don't always catch that great lightning shot the first time around. I'll save some of them in a temp file, delete the rest, making sure I put the FSScreen shortcut button in another temp directory before deleting them and start over. If it's a morning or dusk shot, I'll back up the clock several minutes and go at it again.
Hope this helps.
One other thing: when in slew, you can watch the clouds move.