BULB mode controlling over Lightroom

You can get a relatively inexpensive manual remote trigger similar to this: http://www.adorama.com/UXMC30.html

Or you can go with the Nikon version for quite a bit more: http://www.adorama.com/NKMC30.html

I've used an aftermarket trigger on my D300 for several years with great success. Also, I'm using the links to Adorama not as an endorsement or suggestion to buy from them bet as an example of what's out there. Any good local camera store should have remote triggers; I think I got mine at a Ritz or Wolf camera store near where I live.

Another suggestion, more of an idea to research. I haven't done any long star trails, but somewhere I believe I read about people doing multiple shots at shorter times (i.e. 1 or two minute exposures) and then combining them in photoshop or elements. A 2-3 hour exposure would probably produce a lot of noise. I'd definitely go with relatively low ISO like 200 or 400. As I said, I don't have any experience doing exposures that long, so I can't speak with any authority. If you do use the shorter exposures, remember that, if you have noise reduction turned on in the camera, it will take an equivalent amount of time as the NR function processes the picture. I.e. If you do a 6 minute exposure, it will take 6 minutes in the NR function as well, hence you won't be able to take another shot before it finishes the NR.

Good luck... I look forward to seeing your pictures.