Hi Lance,
The "Add New Host" button was added in later versions of the PlanetPress Design, and it might not be available in 7.2.1. I would suggest to upgrade to 7.5.3. (you should also upgrade the Workflow if you upgrade Design)
If you don't want to upgrade for now, then you'll need to do "Save to file" to save the .ptk file on your hard disk, then manually transfer the .ptk file to the Workflow server and from Workflow do Import->PlanetPress Document. Not as convenient, but it will work.
Regards,
Raphaël Lalonde Lefebvre