do-with-mirrors

Verb

(idiomatic) To perform a magic or optical trick with the use of hidden mirrors, implying trickery and sham.
(idiomatic) To jokingly pretend that one did something using magic mirrors, that one is a magician; a joking explanation of the fantastic or the unexplained.

Origin

Akin to the idea that mirrors can project images and once considered magic. Magicians use mirrors to make things look like magic, thus "do it with mirrors." Today, the phrase is more of a joking pretension that one can make things happen with magic mirrors.

English Wiktionary. Available under CC-BY-SA license.