Equivalent of difftool.prompt per tool?

Is there a way to specify difftool.prompt on a per-tool basis, without manually passing --prompt or --no-prompt to override the global difftool.prompt setting?

I generally want `difftool.prompt = false` set, but one specific tool I use has a high startup time and I'd like confirmation before launching it.

If this isn't possible today, is difftool.<tool>.prompt something others would find useful?

Thanks, Ryan Zoeller