LOL
what a muppet.. thanks mate
correction..
global_start appears to be way too late. There are two that seem to run earlier than this, and neither of those are early enough either.
ok.. I've whacked the $specialtemplates[] = ... into global_start..
but the variable is empty when the header template is built.
when I had identical set-up, but instead of global_start, I hacked the line into the start of the global.php file it worked fine.