How Proximity Sensor Switch Works?

[-TiTAN-]

Hi,
I've got a SGS i9000 with broken proximity sensor. It causes black screen during calls.
Been using MIUI Roms for the past months which can switch faulty sensor off.

I wonder how this switch works? What kinda change does it make to turn that sensor off?
And is it possible to use the same method on other ROMs such as CM10?

Thanks in advance