Hard wiring is actually quite simple. I had my road hawk installed into my e93, i've since removed it and put it in my new car. I did a how to for installing it into my new car but it is pretty much the same on the e90 platform.
http://www.208ownersclub.co.uk/forum...topic1100.html
To get the glove box out on the e90 you need to take the cup holders out.