So, rather than beg for help again, I spent last night figuring it out myself, aided only by a few clues here and a picture of a suggested "scaffolding".
To avoid anyone else having to go through the same trial and error as I did (and to "give something back" to this forum, since I'm new here), I documented my efforts and the result here:
Click for my Brickshelf folder containing text and image guide, and sample lxf files
I did this to create the Alien Conquest "Alien Commander" minifigure, but the same procedure would likely work for any minifig requiring multiple "neck accessories", such as LOTR Gandalf (beard+cape) or Imperial Soldiers (epaulets+backpack) from the old Pirates theme, with a bit of tweaking.
I've also uploaded some completed "head/neck/accessory assemblies" (templates) for people to download and use as-is (and avoid having to do all the steps) below:
Click for my Brickshelf folder containing over 35 lxf "neck assembly" pieces
This includes templates that will allow you to build LOTR Galdalf (beard+mantle) and Imperial Soldiers (epaulets+backpack), as well as a dodgy-but-workable assembly combining an Air Tank with an Insectoid Helmet, for use until the LDD collision bug for those parts is patched.
Anyway, I hope this is okay to post (and okay to post in this format, as a link), and I really hope this proves useful info to somebody! My images/explanations are probably not the best, but hopefully they make enough sense to help someone attempting this to figure it out too.
All in all, a fun learning experience going "outside the box" with LDD!
Edited by Banjo, 22 September 2012 - 02:54 PM.