Converting keyword tags to captions

I'm facining an interesting challenge.  I want to post a large number of images to SmugMug, which I've found to be the best photo gallery system for my needs.  It's a terrific site for photographers to share materials with clients, but one problem with SmugMug Websites concerns metadata.  SmugMug can display full metadata generated by Lightroom, but if you add any restrictions to a site (password, not appearing in Web searches, etc.), it will show all metadata EXCEPT keywords.  But it WILL show titles and captions.  Is there any way to convert Lightroom keywords into text in the caption metadata area?  I have approximately 6,000 photographs, so I'll need some way to make this change as a bulk action.

Any advice on this would be great.