Caption Setup - Source & Job Identifier IPTC metadata fields

I've tagged images in a Lightroom catalog with metadata for a variety of fields, including the Source and Job Identifier IPTC fields in 2600 of the images. 

I want to include Source,  Job Identifier, and other metadata fields in my captions for the images I am using in InDesign. However, in InDesign's Caption Setup dialog box, the Metadata drop-down menu does not include Source nor Job Identifier. 

I'm pretty adept at Lightroom but just learning InDesign.

The only workaround that has come to mind is to use John Beardsworth's "Search Replace Transfer" plugin to Lightroom to assemble a caption via its Caption Builder tab, and then just use the Caption field in the Caption Setup dialog box.

While that may be suitable, I am looking for other options, since I am already using the Caption field for a shorter caption in the image metadata.

 - Rick