I'm no expert, but here's one I did of Lemmon last year. You create two sets of aligned images - pixinsight is really good at this. One set you align on the comet nucleus, and the other on the background stars. When you stack the two sets you use a very strict rejection tolerance and produce two images - one of the comet, and one of the background stars. Then if you've used the same sub as the reference for both processes you can just add the two images together.
http://www.astrobin.com/32255/C/
hope it helps,
Cheers,
Andrew.