I built my own trigger using a circuit from
http://www.solorb.com/elect/lightning/ Works good during the day, but I tend to use the "old fashioned" method for night time stuff. The critical part is the shutter lag. On my Canon 400D the shutter lag can be quite long, I think it was something like 100ms or so. This is very hit and miss with lightning. If the Lightning pulsed then I could almost guarantee I would get it. But many types of lightning have various effects. If you are running an IR system to release the trigger it may be similar to my 400D or slightly longer, only experimentation will prove if it will work or not. During the day I also use an ND filter so I can slow the shutter speed down a bit, just in case there are secondary bolts.
The triggers you see attached to the hotshoe are only there because of convenience, it's just handy to have it sitting there pointing in the same place as our lens. My trigger uses a 9v battery which powers the unit for months. Handy since I have large switches and sometimes they get bumped on.
I think by what I have just read the NEX-5 only has IR remote, so unless you hack into the camera you can only use the IR to control the trigger. So looking at the image above if you use the trigger in place of the intervalometer then you should be able to trigger the cameras shutter.
The circuit above is very adaptable and can even be made on breadboard, I made my own PCB but I cannot find the drawings for ir now... Here are some pics of it, which may help..
This was the first one I made, I modified the box to make it fit better.
http://i363.photobucket.com/albums/o...tpcblayout.jpg
Here is the finished unit on the camera.
http://i363.photobucket.com/albums/o...trigger001.jpg
and here is a strike taken by the camera/trigger
http://i363.photobucket.com/albums/o..._untouched.jpg
and...
http://i363.photobucket.com/albums/o...ther/lls05.jpg
All taken with the 400D and the trigger.
If you want to shoot lightning at night then there are other methods you could try, if you want help with that let me know so I can look up the manual of the NEX-5 to work out a plan.