It's probably the only way it would work - to show top matching snippets from training data on request, with links to the source and ideally licensing information, if it can be gleaned automatically. This would also clearly show how much it is copying verbatim and what exactly is its contribution.

The funny part will be when all the human programmers who steal code will get doxed as a side effect. It shine a light on lots of skeletons in the closet.