Die Fritz!box 4040 kann ueber den 'EVA Bootloader' via FTP geflashed werden.
When this device is powered on, the EVA bootloader allows FTP connection attempts during a certain time frame. The FTP server can be reached at IP 192.168.178.1, so give your workstation the IP 192.168.178.2 and try to connect to the recently powered on device after a few seconds. [1]
Beim Freifunk Darmstadt gibt es bereits ein script zum flashen: https://github.com/freifunk-darmstadt/fritz-tools/blob/master/fritzflash.py