I would love to use a similar line when the gabbai come to ask if I want to daven for the amud. "No, it's ok, you can do it."
As a Gabbai who's having a very hard time finding a Ba'al Tefilla, and Davens pretty much all Tefillos (Shabbos and Weekday) for the Amud, I sincerely thank you for not actually saying it, it's one of the most annoying responses (tied with "Ahem, I can't, my voice isn't the greatest")