You can download a flash image which boots from a connected USB device here. If this image is flashed into the router, it'll try to use a connected usb storage device as a root filesystem.

A root-filesystem to boot the router off is downloadable here. Instructions on how to use it are below, though Dutch readers might want to check out this and this.

Features:

Installation guide: Needed: a Linux-workstation (you might get away by downloading and booting off a Knoppix CDROM, so you won't have to touch your HD) and an USB-mass-storage device (USB-pen, cardreader+flashcard, USB hard disk, ...) which doesn't contain data that shouldn't be erased

Use a root-login on your Linux-machine:

At this moment you can unplug the USB-device and plug it into your router. Apply power and the router should boot.