Interior Trim

I would like to take out the vent in the centre top of the dash, that the handbook refers to as ventilation for the cd player. I want to cut it slightly to feed through my GPS antenna lead. Has anyone removed this themselves? Is it just a push fit or do I need to get at any fixings from underneath by removing the radio.
I have not yet got any radio removal keys, hence why I am asking for advice rather than just taking out the radio to look for myself.
Any help much appreciated.
Rgds
Richard58
Discovery TD5 (2000 model)