Script to customize 'Description' from Keywords?

I process multiple image galleries of 100-125 images on a daily basis using Bridge, and I add keywords to these images which then get converted to Wordpress tags when uploaded to my site. What I also want to do is add meaningful 'Description' (alt/text) to my images using the keywords I already have for the images.

For example, let's say I have 3 images in a gallery titled - 'X-Men Movie Premiere'.

Image001.jpg has keywords Hugh Jackman, Bryan SInger

Image002.jpg has keywords Hugh Jackman, Bryan SInger, Jennifer Lawrence

Image003.jpg has keyword Jennifer Lawrence

I want to be able to run a script that takes the keywords and append it to the gallery title or a customized text and make it the 'Description' for the image. So in this case,

Customized Text = "at the X-Men Premiere"

Image001.jpg should have description Hugh Jackman, Bryan SInger at the X-Men Premiere

Image002.jpg should have description Hugh Jackman, Bryan SInger, Jennifer Lawrence at the X-Men Premiere

Image003.jpg should have description Jennifer Lawrence at the X-Men Premiere

Any scripting gurus that can help? Thanks in advance!