After messing around a bit with TCL, I finally figured out how to read the compressed headers from Giganews. Yay.
Thanks to a post over here, I was able to start with the basic NNTP conversation and add the rest I pieced together over the past couple of nights. My version with compression and SSL looks like this:
Feel free to take the results and run. I'm not sure if there is a limit to how many headers you can fetch in a single go. I imagine it's more or less limited to your local buffer size, so don't grab too many at a time (at least in TCL I imagine). Anything more aggressive would require some fine tuning no doubt. But this was all just proof of concept to see if I could make it work. Now to write my newzbin.com replacement!