The small blade from an original Swiss Knife will work! Best, you have two knifes. The sharp side must show to the outer side from the radio. Push it staight in there.
If you only have one Victorinox knife: Start with one side and try to tie the radio out a Millimeter and then try the other side.
But your dealer will release the rado for free, I think.
thanks for the offer. it is bit late for today because I have to go out in my works van at 5.30 and I think first I will have to stop my car becoming a swimming pool first, (see my other question about water leaks in rear n/s footwell)