Since we were hosting a small business meeting, I decided to cook the risotto to near completion, just short of al dente, before our guests arrived, then put on a lid and left it at room temperature for an hour or so, returning at dinner time to finish it over heat with a little more mushroom broth, butter and Parmigiano-Reggiano. I hoped this wouldn't post an unacceptable risk, and as it turned out, the finished product's texture was fine. I think it was more prudent to do it this way than it would have been to finish it early and then try to reheat.
So, this approach worked well for me, but there's always room to learn. If you've tried pre-cooking risotto and then finishing it later, I'd love to hear your tips and techniques.