I'd push back on this: I wouldn't share something I haven't checked, yet my natural writing style is nothing like Gemini, so having a whole paragraph in a different style in my mail requires a disclaimer (I don't want people double guessing what I'm quoting or if I had some different intent writing that paragraph)
Rewriting it in my own words would clear the issue, but then why am I even using an AI in the first place ?
If I were to include AI generated stuff into my communication I'd also make it clear as people might guess it anyway.