When Villa-Lobos added a cadenza to the Fantasia Concerto he wrote for Segovia, he changed the name to Concerto for Guitar and Small Orchestra. The orchestral writing is 'thinly scored' to allow an un-amplified guitar to be heard, but Mme. Segovia still insisted that she couldn't hear her husband during the rehearsals for the premiere. Villa-Lobos conducted, going from p to pp to ppp, I'm sure with his mouth firmly closed all the time.
This picture, from the Museu Villa-Lobos, is included in the excellent liner notes to the equally excellent new Stein-Erik Olsen CD Havana Rio Moscow, with the Academy of St. Martin in the Fields conducted by Terje Mikkelsen. Incidentally, the album just showed up today at The Naxos Music Library.