I thought the problem with using hook parse_templates is the template will be loaded for every page load, even though it is only required for threadbit?
Either way, the problem has been narrowed down to registering the variables within the template - obviously creating the template is working, as it is appearing in the debug information, but registering it is not. Will try to move the register to another hook, and report back on what happens
--------------- Added [DATE]1262373019[/DATE] at [TIME]1262373019[/TIME] ---------------
Ok, I can't move the template to parse_templates, as it needs access to a function which isn't loaded by that hook.