To make /system writeable, you must install the module and then remount /system as rw.
mount -o remount,rw /system
You can make an init.d script to load it, or add it to the boot.img. Either way will work, but it's important that this is loaded at boot, as attempting to make changes to /system and then installing this module could corrupt the partition.
This is mainly for devs, who are free to incorporate it into their ROMs.
Unless you are an advanced user, I would wait for it to be included in your favourite ROM.
A credit and a link here so people can thank me in the OP would be much appreciated
Source code: wp_mod.c