Mark,
The watermark that our software puts cannot be altered, for it is intended to mark documents that were printed with unlicensed software copies or printers. It is a software protection watermark, and not a feature that is intended to allow peoples to add watermarks to their jobs.
PlanetPress supports the "outline" style in text boxes, so you could create a text box, enlarge the font, apply the "outline" style and then change the "angle" property in the basic attributes if you want it to be rotated. This will give you something similar to the PlanetPress watermark. Then you just have to place it on top of your page.
Regards,
Rapha