The January, 2006, issue of Genii includes a nice production of three coins by Jean-Jacques Sanvert aptly named "Anti-Fly." As the article states, the coins can be produced as a prelude to "Three Fly."
Gregg Webb points out three ways Sanvert's production can be used for versions of "Three Fly" that require an extra coin:
1) Have the 4th coin sleeved. Lowering the hand after Sanvert's production enables you to load the extra coin.
2) Or, keep the extra 4th coin in a clip under your jacket hem.
3) Finally, you may opt to vanish one of the three coins at the end of the production and retrieve it from your pocket. (Actually retrieving the 4th coin.)
(Gregg's e-books, which include variations on Three Fly, can be downloaded at http://feenx.net)