have you tried shutting the aperture right down and exposing for longer?
the smaller the hole the longer you need to allow enough light to come through...whether or not this would work i'm not sure...
you could aslo try the bulb setting
when I took pics of the opera house (admitedly not waiting for lightning) the best results I got were at F8 and F11.....and that was ISO 100 yes I did have some light from the rising sun but it was pitch black when we started to take the photo's
All I can say is give it a go

