Maybe doing the watermark as a signature in the lower corner of the image. This is how i do it. It makes the art have more value because it makes it seem like it is signed by the artist. I show it here with my signature as my name with a .com but it can just be a signature. I made the signature with my wacom tablet in photoshop on a layer and threw away background layer and saved as a PNG file.
I appreciate the response, but as I mentioned in the original question, that's not what I'm looking for. I know how to create a watermark on my images. I have a client that very specifically does not want a watermark on top of the image, it has nothing to do with what is contained in the watermark, they want it below the image so the whole thing shows.
I have created an automation in Photoshop to accomplish this, but it takes a lot longer and requires my intervention with each image so I'd rather go with Lightroom if there's something already in place.
Check out the print module in LR. You can customize a page size, and a smaller cell size for the image. Place the signature on the page below the image. Print to a jpeg file instead of a printer.
LR2Mogrify will let you extend the canvas (of any colour) and place metadata as a caption/watermark where you like. The plug-in is configurable to export a jpeg to use as you require. http://www.Photographerstoolbox.com If on PC installation of LR2Mogrify involves adding imagemagick using a legacy version - follow the links with Mogrify - you will be surprised by Mogrify's power even if there's a learning curve.