Its easy and a cheap mod, just send away your TV module to be re-coded. A compyany called Pegasus sound and light did mine, and from recollection it came to £40 including postage.
http://www.pegasussl.co.uk/unlocking-unlocking-p-256.html
Link above lists it as for an X3, but I couldnt manage to find the right link for the Z4.
I can thoroughly recommend them, I send my tuner and had it back within 4 working days. Worked 1st time, and has been fine since.