It will be wired in to the tape deck, so you many need to use a pen to push the mechanism in. Will all depend on how the hack has been done. If you have a cassette, you could also take the insides out and push that in.
Sounds like someone has done this http://www.350z-uk.com/topic/45398-how-to-bose-phono-ipod-hack-guide/
You will need to follow the cable and see where it goes
If you have the 1.6mm across the 3/4 centre of the tyre . . that is technical the maximum of the legal limit, a lot can depend on the person doing the MOT. If your inside edge to the 3/4 is completely bald then expect an advisory or worst case a fail.
If your running your tyres like this TBH you get what you deserve. In the wet they will be nearly as good as an ashtray on a motorbike and your not only endangering yourself but others around you.
Just put your had in your pocket and get some new ones