Modifying autocp-start

Hi everyone :)

I'm looking for a bit of help. I need to modify the autocopy script that is run when inserting a USB Device. Here's what I need it to do, in order:

1. Copy contents to HD (already does that)
2. Erase all files on the USB device
3. Write a new file from the HD to the USB Device

I've setup telnet using some instructions found on the forum, and I found the autocp-start script. I've managed to edit it by copying it to the HD, but I can't write it back or make a symbolic link because of the read-only filesystem! How can I put my new script file in the place of the old one?

Cheers,
Phil