Hi Mike,
Yes, there is a trick! You have to turn it on your lathe! [8D]
Actually, making a custom centerband is only limited by your imagination! It depends on the kit you are using and how the centerband is used in terms of functionality of the pen. For instance, the centerband on a standard slimline kit is pretty much just for looks. If you want to take one of your slimlines you've made and just eliminate the factory centerband, it will work just fine. This really open up your possibilities with this kit because there are really few restrictions on the custom band you produce.
I have an article on this site that might help explain how to make a basic custom centerband. Here's the link:
http://www.penturners.org/content/aaw-winter03-36-41pens.pdf
If you're using another type of kit, let us know and someone is sure to jump in and suggest some neat modifications that might suit your purposes! Good Luck!
Scott.