Well, I figured it was time to come good on my promise so I grabbed the kernel source and started reading Nokia's Kernel Guide.
Anyway, after making unsuccessful modifications to drivers/misc/nokia-av.c and sound/soc/rx51.c to try and force it to enable the button even if "a normal pair of headphones" are plugged in (my understanding of electronics is even worse than my coding skills), I realised that having the mic enabled along with the button are mutually exclusive (this "bias" stuff).

Since my attempts at hackihg the driver failed, I looked at what was actually doing the disabling on the users' side: the Policy system. Did a grep in /usr/share/policy for "bias" and found a text file that could be exited. Made disabling the bias the same thing as enabling it and rebooted it in hope.