Andy - If you have access to the deployment packaging for Omniscope in a corporate setting, there is a configuration file switch that will suppress the free trial. Steps on how to do this are documented on the following KB page under "Disable free trial" section:

http://www.visokio.com/kb/installconfig

If you do not have that level of access/control over a mass deployment, the alternative is to use a list of free Viewer keys. Currently, you are the only ones using the admittedly labour-intensive free Viewer key method. Having an easy-to-remember generic free Viewer key might speed the task (important when you are doing 50 free Viewers) but this would be difficult for us to implement since the activation logic and information contained in the license keys is complex and risky to override.

Remeber that the free trial option only appears when users open the Viewer empty. Clicking an IOK file attachment or download link with the free Viewer installed does not display the free trial. Also, owner-locking an IOK file prevents any changes to the file, even by users with activated free trial or any fully-licensed, activated Omniscopes.