Several times in the recent past people have asked "If I have a bare-bones Arduino project in a remote installation, how do I send a new sketch to the site in such a way that someone there can upload it to the Arduino without having to install the Arduino environment and having a USB-to-Serial cable?". This article just published in Hack-a-Day might provide a solution:
http://www.hobby-roboter.de/forum/viewtopic.php?f=4&t=128&p=531
http://www.hobby-roboter.de/forum/viewtopic.php?f=4&t=127
The article is about a Java program that will convert a .hex file to a .wav file and an Audio Bootloader that will allow the ATmega chip to interpret the audio in the .wav file. Send the .wav to the remote site and have them play it through a cable to the Arduino. The only cable they should need is a mini phone plug to mini phone plug cable. They might even be able to copy the audio to an iPod and play from there.