TV on the move

I am in an S5 at moment but thinking of S8 (08 model year) as there are some half decent deals around. I previously had an '06 A8 with TV but never got round to getting TV to work on the move as an auto electrician told me it needed a piece of kit cosing several hundred to get it to work.

Do you know if that is nonsense as it would appear from posts elsewhere that on older models, at least, the trick is to get the unit to think the vehicle isn't moving by disconnecting / cutting a wire.

Any help much appreciated

Futura Blue