Is there a way to put a watermark diagonally across a photo without creating a custom one in photoshop?

I don't know of a way to rotate a watermark using Zenfolio's toolset.  I have diagonal watermarks on mine, but that was because I did it myself and uploaded the text pre-angled. 

Do you have photoshop or something similar to create one and just don't want to?  Or do you need someone to create one for you?