Do you mean you want to use the automatic feature within InDesign to place captions, but not feeding the mechanism with metadata from the image but with a different source of contents?
One could write a script that would fill in captions from a different source, if the metadata of a placed image would not provide valid information after running the automatism.
On the other hand:
What you could do is using InDesign's Data Merge functionality for placing images and captions from a tab delimited text file or a csv file you prepared in a text editor or in a spreadsheet app like MS Excel.
I guess what m trying to do is much simpler then that. I'm creating both txt and graphics 'boxes' and placing information or graphics with no imbedded data. I want to be able to simply add a caption to the frame and provide the text myself. Then I can use the caption as a marker for cross referencing or a 'figure' table of contents.
As I think about it, it may be a simple mater of extending the frame and simply putting the information I want in the old fashioned way.
Yes, basically there is nothing special on the text frames, the containers for the text, InDesign is building with its automatism for captions.
You could use them like "normal" text frames…