Crossroads makes a board that loads a selected hex file from SD card to AVR chip.
http://www.crossroadsfencing.com/BobuinoRev17/Programmer.html
Three versions available: single file programmer with no display ($41.50) (not pictured yet); one display programmer supporting up to 16 files ($45.25); two display programmer supporting up to 256 files ($48). Contact us to order one. All boards include a Sandisk 4GB SD card and 6 inch/15cm programming cable. Shipping & paypal fee added to all orders.
The project is part of a Nick Gammon blog, Bob collaborated and the result can be purchsed and used.