Edit a file on a ext2 USB key that is read only

I have a USB key with files onto it that are the filesystem of a Debian server.

I need to edit /etc/hosts to fix a mistake I made (the server has no screen nor keyboard, so because of that mistake, it is unreachable through the network for SSH now).

I plugged the USB stick on my Mac (I have MacFuse and fuse-ext2) but the disk is read-only, I can't edit the file.