It's been a while since I tried 3D models and Chilli Source, and being a programmer I wasn't very good at doing a lot. I do recall there wasn't support for null nodes or creating a model consisting of empty nodes. Has this since been added? I know the model stuff was updated to support Blender but wasn't sure what else had changed to support the wider collada format.
I'm looking at going back to my model stuff and was just wondering what's now supported. My fallback is to create a blank model in the right shape and use the attachment points to actually attach my sprites too to create a 2D looking object, build up in 3D space using a model for structure and animation.
The effect I'm trying to get is the same as the old After Effects animation system, or the same system used in Moshi Monsters and Cat Tap Fever.
The animation system is currently purely for skinned animation so it isn't geared up to handle scene/node animations like you are attempting. That said, your work around sounds like it should work: Just create a single triangle mesh and skin it with your node animation. In game, add a fully transparent material to the cube so you can't see it and attach your sprites to the nodes. Make sure you only skin the root node for the sake of performance!
As mentioned before, we will be adding support for scene/node at some point - it's in the backlog, along with a number of other animation system improvements (including overhauling the Collada conversion tools as they can be a be a bit fiddly when working with animated models). It'll be a few months before we get to it though unfortunately.
Not the answer I was hoping for but at least with the new support for Blender I can get the work around in! The animations will be super simple (note my previous admission to being bad at modelling) so it shouldn't be too difficult to update at a later date if I need to.
Thanks for the help.