You need to root your device, and yes that was my main motivation so far for doing this. Note : be careful to flash the correct boot partition for your wifi/3g model otherwise you will softbrick it like me :-)
With root explorer or a shell, remount / rw
(you never know you suddenly want this atrocity back)
Copy over one of the other font present on those 3 files, ANY other font would look better. I took DroidSans.ttf.
Jump to the lock screen (press power button once) to testdrive the change. If it works as expected reboot the device and it will change it also on the bottom bar.