I haven't found a way of condensing a caption, but there may be a workround.
Is it an online document or printed?
How many words are there in the captions to the pictures/diagrams?
If there is a lot of text, would it not be better in the main body?
Would a strict
précis of the caption not be in order?
I lied, 4 things.
PS. Edit 8 Dec.
Why not insert a caption as normal, but with minimum explanatory text for the ToF. ie: Figure1.........Electrical Busbar Flange.
Then in the main body of text, insert your full text relevant to the image/diagram, but formatted with a different Heading Style, centre justified, italic, for instance to make it standout.
You would have the shortened ToF in your document (with your brief text), but the image in the document can all the words you want.