do you have access above the docment root?
if so you can do some really good stuff!!!!
I have FTP access to:
/
thepeccavi.co.uk/ (files displayed on that domain name)
shadowideas.thepeccavi.co.uk/ (files for that sub-domain)
If you had:
/
yourdomain/ <FILE to access IN ROOT!!!>
yourSECUREdomain/ <FILE IN ROOT!!!>
then on you secure domain you could do:
include('../yourdomain/filename');
this assumes that both files concerned are in the root directories of their domains...
NOTE!!! "../" means "go up a directory"
Hope this helps!